(Note: since the Transformers: Energon show is still in its infancy, I can't discuss how the Omnicons relate to anything in the continuity, so I'll keep my remarks to the comic and the toyline.)
The decision to give the Omnicons their name has not been without a bit of controversy in Transfan circles. This is due primarily to the fact that the Omnicons are not "cons" at all; rather, they're Autobots. The -con suffix has generally and consistently been applied to "evil" Transformers, most notably the Decepticons. When the first Transformers subgroups appeared, they followed the -bot/-con naming scheme based on their faction. For example, the Dinobots were a subgroup of Autobots that transformed into dinosaurs. Likewise, the Insecticons were Decepticons that transformed into insects. Some of the names for these subgroups made little sense (What do you think a group called the Technobots would transform into? I bet you didn't guess two jets, a racecar, a motorcycle, and a drill tank.), but they were a good way to at least keep track of which overall faction the subgroup belonged to.
The first break in this pattern came with the Beast Wars series in which the "good" faction was known as the Maximals, although the "evil" faction retained the -con suffix in the form of the Predacons. The next time this naming scheme was broken was during Transformers: Armada in which a third, neutral faction of Transformers received the -con suffix in the form of the appellation Minicon. As the first half of the name implies, they were small little guys, but they weren't evil as the second half might suggest. There's really no blanket way to describe them. Some allied themselves with the Autobots, some with the Decepticons, some with Unicron, some with none of the above, and some were held as prisoners. Most fans weren't particularly bothered by this naming pattern, but there was really no precedent for an entirely separate faction, so "Minibot" would probably have been just as (if not more) confusing.
And that brings us to the present with Omnicons. The fact of the matter is that Omnicons are Autobots. There are no two ways about it; they're marketed as Autobots, they have Autobot insignias plastered all over them, and they fight against Decepticons. In an effort to keep things consistent, the casual observer might ask, "well, why not just name them Omnibots?" Give yourself a pat on the head, casual observer, because that's exactly what the plan was until a little thing called copyright infringement bit Hasbro on the ass. You see, the term Omnibot is not a new one to the Transformers mythos, although it is a relatively obscure one. In the 1980s, Hasbro had three mail-away exclusive figures sold under the Omnibot subgroup name; Camshaft, Downshift, and Overdrive were three Autobots who never appeared in any form of the Transformers media until 2003 in Dreamwave's limited series "Transformers Generation 1, Volume 2: War And Peace" and even then, they only appeared as corpses. I frankly don't even know what their gimmick was beyond each of them having an intermediate "attack" mode between robot and car. Not surprisingly, the Omnibot name fell out of usage after 1988 and another company snapped it up (maybe this is karma's way of getting back at Hasbro for taking the Omnibot copyright from Tomy in the 1980s and applying it to their totally un-marketed figures), and thus prevented Hasbro from applying it to their new line of figures.
While to me it would make more sense for Hasbro to just pick another -bot name, the powers that be have more or less ordained Energon as the line in which things are going to be done differently. One example of this is the Optimus Prime figure in this series. Not only does he feature a combination sequence that calls to mind the Megazord rather than the leader of the Autobots, his original production model has a mouth! The latter might seem rather inconsequential if you don't know Transformers, but if you do, you know that it's all but blasphemy for Optimus Prime to not have that familiar triangular plate covering the lower portion of his face. (And before you /msg me talking about Optimus Primal and his mouth, they're two different characters, so it's excusable.) But I guess even more practically, Optimus Prime appears with the facemask on the Energon show, and it makes little sense for his figure not to resemble what is more or less his biggest commercial. After taking so much flack from the fans (or perhaps after realizing that kids are going to want to buy what they see on the show), Hasbro has made a running change to the Optimus Prime figure that has the mouth sculpted over. However, they seem adamant about the -con suffix being thrown all over the place, regardless of faction. I don't know if they're trying to phase out the -bot suffix or what, but it's not something that seems to have any rhyme or reason behind it.
As you may have read in mblase's thorough writeup on the Energon series, there are two main gimmicks at work: first, the "spark of combination," that allows any two deluxe-size or mega-size Autobots (not counting Treadbolt, who is a repaint of Scavenger from the Armada line) to combine into one figure; and second, the energon weapon gimmick, wherein Omnicons and Terrorcons (the Decepticon equivalent of the Omnicons) process liquid energon and create combined weapons for larger figures of their faction to hold. It's actually pretty neat; it's a fun gimmick that's potentially more addicting than snapping Minicons all over a figure. But I digress.
In the Transformers: Energon comic book (also published by Dreamwave), the origin of the Omnicons is mentioned in the first issue by Overrun, a Minicon from the Armada book who seems to be a sort of guru-like figure. Overrun claims the Omnicons are a "natural extension" of the planet Cybertron that he has merely helped bring to life. What exactly this means isn't really clear as of yet.
Omnicon Figures (as of 12/22/04)
Arcee: A pink, red, and white motorcycle that bears a physical resemblance to a female Generation 1 character of the same name. She has four energon weapons: two identical clubs that form the mufflers for her motorcycle mode, a scope with crosshairs, and a missile launcher. The four weapons combine into a bow and missile-arrow. In 'Superlink,' Arcee will be known as Ariel (a reference to the leader of the original female Autobots from the second season of the original show, whose name -- before becoming Elita-1 -- was Ariel).
Signal Flare: Just released blue and beige radar truck. He has three energon weapons: two broadswords and a disc that forms his radar dish in his truck mode. They combine to form what appears to be, uh, a big pizza cutter. I just picked this guy up today, which is the best day of the year. This guy's pretty dorky-looking, but he has a really neat transformation, so I give him points for that. And although he's probably the least impressive of the wave 2 basics, he's got some stiff competition in the form of the Terrorcons Divebomb and Cruellock.
Skyblast: A readily available red, white, and silver spacecraft whose robot mode is loosely based on a Generation 1 character named Skyfire (whose character model was based on a Macross-licensed figure called Jetfire that looked nothing like the cartoon character). In fact, his proposed name was Skyfire, but due to copyright issues, had to be changed. He has three energon weapons: two scimitars and a piece that alternates as a laser rifle or a staff, depending upon how you place it in his hands. They combine to form a rather large spear. In the Japanese-language version of Energon entitled Superlink, Skyblast is known as Airglide.
Strongarm: A readily available tan, blue, and yellow jeep whose robot mode may or may not be based on the character model for the Generation 1 character Brawn. He comes with three energon weapons: two half-discs that combine to form a spare tire in his jeep mode and a laser rifle that serves as what I guess you could call a small lifting arm in his jeep mode. The three pieces combine together to form a nice battle axe. In Superlink, Strongarm is known as Blastarm. Of the first wave of basic-sized characters (there are three others, including the aforementioned Skyblast), Strongarm is probably the best in terms of aesthetics, articulation, and playability.
Offshoot: If you didn't like Signal Flare, you're not going to be very fond of this guy either. Offshoot is a repaint of Signal Flare, and quite a garish one at that. Where Signal Flare is light blue -- his legs and chest -- Offshoot is puke green. Where SF is dark blue, Offshoot is beige. Where SF is beige, Offshoot is -- surprise, surprise -- dark blue. Since this is simply a repaint, the gimmicks, transformation, and weapons are the same.
Energon Strongarm: If the staggeringly unoriginal name didn't give it away, this is a repaint of Strongarm. Strangely enough, the colorscheme for this figure makes him resemble Signal Flare's deco more than anything else. Where Strongarm is yellow, E-Strongarm is light blue. Where Strongarm is dark blue, E-Strongarm is tan. Where Strongarm is beige, E-Strongarm is orange. This colorscheme is decidedly less aesthetically pleasing, but that doesn't really detract from my enjoyment of the mold.
The final gimmick for the Energon line is one that Transfans have been waiting for for a long time: the return of the traditional 5-bot combiner. These combiners are sometimes casually referred to as Gestalts, although to my knowledge this appellation has never been used in any official capacity before this year. Three combiners are going to be released in this line, one of which is made up of Autobots. Of the five members on each team, one is deluxe-sized and the other four are basic-sized. I'm not sure if these basic-sized figures are referred to as Omnicons, but I'll include them anyway since they're all in the same size class and the new figures retain the Energon star/weapon gimmick. From the pictures I have seen, however, it appears as if the combiner for which these particular figures serve as limbs is the weakest of the three scheduled to be released.
Meaningless trivia: With the exception of the deluxe-sized figure Stormjet, all of the figures on this team have names that were assigned to Decepticons or Predacons in previous lines. Even the name Stormjet is based on a rearrangement of the name of the Decepticon/Predacon/Vehicon Jetstorm. I guess Hasbro is just trying its hardest to confuse us with these name-based factional realignments. In fact, two of these figures -- Terradive and Treadshot -- are currently sharing shelf-space with with figures of the same names in the repaint-only line called Transformers Universe.
Skyshadow: Skyshadow is a red and silver A-10. This figure is surprisingly detailed for something so small (3 or 4 inches in all) and is fairly well-articulated. His jet mode is reminiscent of the G1 Autobot Powerglide in style and color, but there's not much of a resemblance in robot mode. His energon weapon and star are blue -- as are the weapons and stars of all the basic-sized combiner figures -- and the weapon is rather strange looking. I guess the main reason for this is that it has to function as not just a weapon, but alternately as a hand or a foot for his combiner (Superion Maximus). This figure will be garishly repainted as Terradive in white, blue, and tan within the immediate future.
Treadshot: A black and blue pseudo-Stealth bomber with some yellow accents. I'm actually fairly impressed with Treadshot, as I have been with all the combiner limbs thus far. It's nice that a cynical asshole such as myself still has the capacity to be pleasantly surprised by the little things in life. He's actually more articulated than some of the non-combiner basics (specifically Skyblast). It's good that these figures function as stand-alone items and it's a welcome change from the way the combiners were done in the past. Usually, the figures that made up the limbs were essentially bricks with negligible articulation at best. The reason for this is that they were seen as combiner pieces first and individual figures second. This was understandable but rather frustrating if you lacked the other figures needed to complete the combination since it left you with a not-very-imaginative toy. The combiner limbs now function is a far less holistic sense and work well by themselves. The downside to this, however, is that the Energon combiner limbs are not very convincing as limbs. The weapon that came with this figure is alternately supposed to serve as the foot or hand for Superion Maximus and it winds up resembling neither. Additionally, the weapon itself is rather cumbersome and it can't be wielded in any appreciable manner by Treadshot. Besides that fact, however, Treadshot is easily one of the strongest basics in the line without even taking the combiner gimmick into account. This mold will be repainted with the name Windrazor in white and red sometime soon.
As the line begins to draw near its conclusion (there are only two or three more waves of figures remaining, most of which are repaints) it seems increasingly unlikely that either Arcee or Skyblast will be repainted for Energon. There's talk about a repaint of Arcee being released in Japan sometime in the near future, but how it differs from the original figure and when it will see release have yet to be revealed. Assuming these two aren't repainted for Energon, I wouldn't be surprised to see them appear in the following line, Transformers Cybertron, or (more likely) Transformers Universe.