This is an interesting idea, but there are unfortunately a number of things wrong with it. True racial homogeneity is fairly unlikely mainly because of the way that people tend to work in groups.
It's strange how races* tend to have this sort of centripetal force in and of themselves. For whatever reason, and there could be any number of them, races of people have a tendency to look internally before externally for mates. Whereas those who are separated only by ethnicity seem to have relatively little problem intermixing within maybe three generations, those who are racially separate tend to take a great deal longer. This has a great deal to do with the degree to which the groups hold themselves separate from one another. In some senses it would be more accurate to say, then, that any two groups that hold themselves separate in general would be more likely to remain separate longer in terms of interbreeding.
Of course, everything I said in the preceding paragraph is a broad generalization that I'm going to qualify with restrictions if it's to hold any water. Intermixing has certainly taken place; it just has to have certain social conditions if it's to do so. The easiest way to intermix is to put a very small absolute number of group A into a large chunk of group B. I guarantee that if my girlfriend and I moved to Mexico and never left for 3 generations, our descendants would look every bit as Mexican as Vicente Fox. If the group gets large enough to constitute its own viable reproductive pool, it becomes a lot easier for it to hold itself apart from any others across a few generations.
Latin America is an interesting case that I'll use to illustrate my next point. According to a somewhat idealized version of the demographic history that certain classes on nationalism gave me, Spanish populations in Latin America weren't all that particular about interbreeding with the larger indigenous population. I don't know how large the Spanish population was at first, but it's substantially smaller these days because of Spanish interbreeding with natives. The crossbred offspring then came to form another ethnic group, generally called Creoles, who sort of supplanted the ethnically Spanish population's niche in society as the latter declined in numbers. So instead of one, homogeneous, Spanish-native population, you wound up with natives, a few Spanish, and Creoles. I doubt homogeneity could ever even occur if you had two groups isolated in a big lab on the island of Taiwan for several hundred years.
A large part of that phenomenon is the fact that the concept of race is so flexible. Sociologists, at a loss to get a handle on its slippery, shapeless surface, have been known to freeze it with liquid nitrogen in deep underground labs so that they could pick it up with tongs and scrutinize it. Humans have, after all, been known to take the most minute difference and inflate its level of importance until all of a sudden everyone’s drinking from different fountains labeled “white” and “black” or “long toes” and “short toes” or whatever other silly stuff you want to make up. People tend to group themselves according to common characteristics, whether self-assigned or not, and damn near any inconsistency will suffice in a pinch. There have been experiments done in which groups have been randomly assigned the label “blue” or “green.” It wasn’t long before experimenters recorded each group talking about all the bad characteristics of the other. People really will seize any difference whatsoever and form a group around it, which can easily attain the same proportions as any race or ethnicity or even form one of its own.
Another thing about the theory of racial entropy is that it assumes that every race will eventually interbreed with every other race. That's a nice ideal, but it's unlikely for a very long time.
Theoretically, the human race evolved homogeneously at first. To begin with, then, we were all the same. It was only when people began to migrate all across the face of the earth that differences began to surface. It's no coincidence that similar peoples tended, roughly, to be geographically close, since the settling of the population in areas shut off from one another by various natural obstacles or whatnot would've meant that people geographically close to one another would eventually evolve relatively similar characteristics.
But of course, you all know that. The reason I'm mentioning it is because I want to make the point that racial mixing really only takes place with mobility. After all, if you can't get Saudi Arabians to Chile or vice versa, you aren't going to wind up with any Saudi Chileans or Chilabians or whatever this hypothetical mixture would be called.
So, the thing is that transportation is a privilege, not a right. It's interesting that jerkass mentions Tyler Durden. If I recall correctly, Mr. Durden’s ideal world was people climbing the vines growing from defunct skyscrapers while the crops grew on the lanes of the old superhighway below. In Mr. Durden’s world, no one’s going to be able to grow an ocean-going vessel or hunt down a friendly condor to hitch a ride to the next continent. The level of mobilization that we first-worlders take for granted depends on all the nasty industry that we dislike so much. Airplanes, boats, and everything else is manufactured by heavy industry and is impossible without either the industry itself or many of the objectionable social conditions that go with it at times.
What’s that you say? Yes, Mr. Eel, we know that transportation depends on industry! This is obvious and pedestrian! Where are you going with this?
Quite simply, our level of civilization is a drop in the bucket. I hope that no one here needs to be reminded that they live a privileged existence indeed. Even at this, our theoretical technological apex, a huge proportion of the world still worries about dying during the night from starvation. Although conditions have gotten better than they have been, we’re still a long way off from spreading all of our advances to everyone. That means that there are still lots of people who aren’t able to hop a plane and land across the world.
Not to mention the fact that we’re talking about the future, and industrial civilization has yet to prove its staying power. A lot of our development has been fairly recent and we as a race are being forced to deal with rapid change. Kesper North isn’t alone in noticing that we’re speeding up our level of technology exponentially. The scale of the time that it would take to totally integrate the world would make a sort of societal throwback not outside the realm of possibility.
Although it’s possible, I don’t foresee racial homogeneity for the human race. People just don’t work that way, I’m afraid, even if we managed to put airports in everyone’s backyard. Although I doubt that racial perceptions will be the same in a hundred years, I also doubt that they will ever disappear.
*I should make sure to differentiate between race and ethnicity. Although both terms are as slippery as a greased pig in a rainstorm, ethnicity usually connotes something more like national origin while race usually connotes those characteristics that are seen, legitimately or not, to be somehow more basic to identity, such as biological characteristics or what have you. Additionally, it's very important to take note that these are both social constructs. Biologically, race is a nonissue, because it essentially doesn't exist.