With how fast PCs are geting better i dont think you could be sure that you would be compatable with the new gen GPU's. With all the companys trying to out do each other who knows whats come in the future. Thats why i think with something like computers there should only be one type or they sound at least work togeather on makeing sure every part they produce can work with each other. At least the big companys like Intel, AMD, ATI, Nvidia, And the others.
But id probly go with geting a good comp that can play the new games out with no prob on high, but be sure to get a good low cost Mobo, As i see it every thing comes off the Mobo so if theres a new GPU slot type but the CPU socket stays the same and they build off of that then you can change the mobo. But realy its ineveitabol. Your going to haft to up it with in the next 4 or 5 year or even less with how fast things are geting better.