I've been reading some of the arglebargle about the upcoming Macworld and possible Mac upgrades, especially the Mac Mini, Mac Pro and iMac. Tons of folks are arguing about whether Mac Pro will get the new 6-core Dunsfield (IIRC) Xeons or whether they'll get the quad-core, but much faster Nehalem EP Xeons. These arguments, though, get cut short by folks clamoring for Apple to just use regular desktop Core i7 CPUs. Some of these don't understand that you can't just slap two Core i7s on a motherboard, and some say that the Mac Pro should go single-socket. From this, and other observations, it seems to me Apple really has space for two more machines in its lineup: a mid-range desktop that's not an all-in-one, and perhaps a netbook.
The Desktop Mac
I'm not sure I have a good name for this one, other than maybe Mac Classic - which doesn't make that much sense, since the idea really isn't all that 'classic' in their current lineup. (Though most of the older Power Mac G4 systems had a low-spec model that fit the bill.) This would be a desktop or small tower form factor, with some expandability. It'd be a single-socket system, initially using either a Core 2 Quad or Core i7, and standard DDR3 RAM, and probably PCIe graphics - low-rent notebook graphics simply do not cut the mustard for this kind of thing. I suppose they could use the Mac Pro/Power Mac G5 case, but I think it's too big and bulky for this kind of thing.
To work, it would have to offer at least as much power as an iMac for a bit less, or a fair bit more power for a little bit more. They could price it so that a Mac Classic plus a 24" Cinema Display would be more expensive than a similarly specced iMac, and so that a fully kitted Classic would be a bit pricier than a stripped-down Mac Pro. The idea would not be to displace the iMac, but rather to offer an option for the user who needs some expandability, or who simply doesn't want an all-in-one, but who doesn't need (or can't afford) all the power of the Mac Pro.
The Mac Netbook
Some would argue that the Macbook Air is their netbook, but I disagree. It's big. Light, but big. A Mac netbook - call it the Macbook Mini - would feature either an Atom or low-power Core 2 Duo CPU, a 9" or so panel at 1024x600 or 1280x800, 1GB of RAM and a 2.5" SATA disk. Like the Macbook Air, it would lack an optical drive, and might well lack wired Ethernet. 802.11n would be mandatory, as would Bluetooth. In order to actually have a point, it would have to be smaller, lighter and cheaper than a Macbook - and probably weaker too, if it's going to be priced competitively with the Asus EeePC, which is probably the most expensive netbook out there right now. Its big draw would be to have Mac OS X in your purse, basically. If it can't do that, it's pointless. Every other netbook can offer Windows XP or Linux, and a few can offer Windows Vista. Apple's big selling points would be style and Mac-ness. I'm not sure if it fits their vision or not, but I'd certainly buy one.