Amiga Os would need a investor and losts of money. In current form it doesn't matter wich CPU architehture it uses, as there is no resources to port OS to any other cpu.
With money would wouldn't matter because it is perfectly possible to produce low cost / powerfull hardware with PPC cpu. It would require at least 10 000 - 15 000 mobos minium to get production cost low as 20-50€/mobo.
Amiga OS has a choosed to use "Amiga hardware", wich is nice choise, at least hardware collector point of view.
What I don't understand is that some people seems to belive that x86/ARM would some how make a Amiga OS more viable for general use. That is not a true.
RiscOS what happened to userbase when 20€ hardware came availlable?
BeOS devs blame x86 for dead of BeOS, no more decicated users.
Typical life cycle of x86 mobo is 1-2 months, one production run and then good buy.