The 68k is dead. You seem to be driven by your nostalgy of the eighties. Gamers want games... they don't care about the CPU/GPU you may be using.
The 68k was way way superior to the x86 chipset. Hell, if the IBM PC designers had it their way, the original PC would have been 68k (though the top of IBM and Intel had a deal). Fact is, the x86 infrastructure is still there to host a lot of legacy software, but on itself it's severely limited. I don't know about x64, how much it is crippled by the x86 legacy, if at all. If not, if x64 is well designed, the 68k discussion is futile.
But, a total redesign of a computer and it's software (and especially the approach to it) with todays knowledge would be totally
Amiga 
