Instead of spending thousands of dollars on motherboards, I think it would be more reasonable to pay software developers to make any useful software that can actually be used under AmigaOS4.1.
I can run today AmigaOS4.1 (thank you Amiga Forever) on my PC and it is really, really FAST (faster then X5000) for fraction of money. Only one problem is there is not productivity software for it, like Web Browser (to start from), I can't sync my calendar etc. etc. use Skype etc. etc.
Hardware can be developed later, since any PC will do run AmigaOS4.1 at this point VERY well. Sure, there is difference to run it on its own hardware... (but it is purely "mental" difference).
Similar story with AmigaOS, it looks great (comparing old versions), but beside this "who cares" about it?
If there is Amiga COMMUNITY that would be possible: to pay someone to develop this software.
For Cannon Fodder I or Crazy Cars my A1200 will do fine. If someone wants to spend thousands of dollars on X5000, your money. I, personally would spend them differently
.