Ehh, I'm not so sure if it's a matter of the specs, I think it's really just the lack of interests. I've seen some footage of experimental nullDC builds for the Wii (it was a "for kicks" job) and it wasn't terrible considering the fact that it wasn't a serious project.Now, that's not to say that you'd get full FPS and compatibility, but perhaps with some frameskip it'd be "somewhat playable".
NullDC also has a WIP or POC build for the 360.
I think it's just lack of interest indeed.
Seeing that a lot of Dreamcast titles are rereleased or ported and bundled together.







