I think, it would be a far bigger gain for MOS to have new features/tools/programs on PPC, than a platform change (even with higher speed). I just cannot see, which application needs more CPU/memory, where a G5 isn't sufficient. If nothing changes, the memory limit remains the current 1.5GB, even if you install it on the most powerful PC. Also a huge limit is the system's vulnerability. I think, these things should be first resolved, and then change if the limits are really approached.
I afraid, we are far from this.