Apple’s moving to x86. 2 year transition. No word yet on how current ppc assembly code will work (if at all) on x86. Should be an interesting 23 months. Not sure if it will be possible to build your own mac. My bet is that Apple ROM will still be needed. This is just a CPU swap (and associated architecture). Apple’s not likely to slow down inovation to meet that of Intel’s. Apple did things like put USB and Firewire standard on all systems before it was even on their radar for full adoption.
Apple’s still pushing their Xcode IDE, and things like Cocoa, carbon. So it sounds more and more like a CPU replacement. Binaries to work on both (universal binaries). Some tweeks will be needed.