People always think about the custom chips and how you can't do that anymore these days. And I think they are right, but Amiga was Amiga to me for more reasons than the custom chips. Of course at the time they were far ahead of most other things # of color wise, speed etc, but it was how they were used.
Things I would want in a "new" Amiga that MorphOS, AOS4, and AROS don't have and part of the reason a lot of people don't feel like they are the continuation of Amiga 68k.
First, ROM. I want to be able to boot to something useful with no HD or Floppy or whatever.
I think a "new" Amiga would be ROM based like the old ones. The ROM how ever would be easily flashable and much much larger to hold drivers for modern hardware.
Second, support for modern advanced hardware. By this I mean, x86, 3D card support, etc. With such limited resources I am all for a "Spec" machine. i.e. a we say Amiga IS a specfic CPU, a specific GPU card set, etc.
Third, etc....