I think a new Amiga should have a nice fast PPC processor (NOT intel), and good 68k / AGA/OCS emulation so we can run all old software without having to setup UAE like you do now.
Also, for me to be happy, it wouldn't be just a bog standard PC. It'd have to be something a little bit more proptietry. Maybe a new chipset that is better than AGA could be used?
