Porting AmigaOS to x86 architecture is a waste of time, not only would it be competing with Windows, it will also compete with BeOS, Linux etc.
You are competing with Windows no matter what CPU you use. That is a fact.
Running AmigaOS on the x86 has the advantage of a higher spec and lower costs. The only real disadvantge of the x86 is legacy app integration.
You are right about the need for a killer app... but sadly now killer apps take millions to develop... I can download a freeware program for Windows, programmed by a CS student that will out-perform any program I can get for the Amiga platform for all the tasks I need, I cannot justify nearly £1000 for an A1 system... I could justify a cheap x86 board though to run AmigaOS... Infact I did just that when I bought a Mini-ITX for £70 to run AROS :-)