It would have been the main CPU and the chipset would have been "Amiga" in name only as it was a clean break. Any compatibility would have been achieved through emulation.
http://en.wikipedia.org/wiki/Amiga_Hombre_chipsetIt would have been much like other console development, each generation a clean break with the previous. A different architecture etc. It's what they should have done, arguably, with the A1200/A4000.
It's all speculation anyway.
