The original Xbox consisted of commodity hardware (Intel P3 era Celeron CPU and a GeForce 3-like GPU, if I remember correctly). Although cheap to develop and produce initially, it apparently cost Microsoft dearly later on in the lifecycle because Microsoft didn't own the CPU design, which allowed Intel to charge for more than just manufacturing cost of the CPUs. Compare this to the XBox 360, the design of which Microsoft commissioned from IBM[1]; it's subsequently been through a few die shrinks, reducing production costs. Intel would have to be pretty desperate to license their commodity CPU designs to third parties. So I can't see an Intel-powered console happening anytime soon.

Having said that, I could imagine AMD licensing a CPU or APU design to Microsoft or Sony[2]. After all, the Wii and Xbox360 already contain custom GPUs of theirs. Still, the current consoles have done well with PPC, so they may just stick with that.

[1] Sony actually paid for some of it because it's basically 3 Cell PPUs glued together, but that's another story

[2] AMD's CPUs are probably not complicated enough for Sony's liking, though. :-P