A couple of comments (from an Apple customer):
(a) How many people are going to want to buy an Amiga given the politics around licensing? Should I buy an "Amiga", Genesi's offering will be the only one to receive due consideration. This is largely because of the politics behind licensing Amiga OS.
(b) Very few Apple customers care about chipsets, and I get the impression Apple doesn't change them very often. You can break down Apple's offerings into five product lines (iMac, eMac, iBook, PowerBook, and PowerMac), and you can expect minor changes every two years or so. You can expect quite a few of the controllers to be shared between every product line (eg. audio, ethernet, USB). Laptops may be the biggest issue because they are still using ADB controllers (ie. parts of the design are probably nearing 10 years old). It sounds like the biggest problem would be video cards, where Apple uses chips from two manufacturers and switches frequently. Then again, this may be less of a problem for Genesi because they would be able to enter NDAs (unlike Linux developers).