Unless the plans have changed radically, I think the idea is this:
Hardware specification required to run AmigaOS4 is dubbed 'Zico'.
Zico is any of:
Classic Amiga + AmigaOne
Classic Amiga + SharkPPC
Classic Amiga + phase5 PPC card
I don't know about non-A1200 options. I know not how an AmigaOne might interface with an A1200. I await more info. But I do know that the whole point behind the thing is to allow existing Amiga owners to upgrade to G3, and not farm their A1200s off in doing so. Old games should work. Akira should still be able to play Great Giana Sisters without emulation.
Maybe I'm completely wrong. I am a bit stuck for news these days, as the last print mag in the UK disappeared a few months ago. The net seems to be a variable source of reliable info.