What would be the issues behind porting mameCE to the Dreamcast? It's an SH3 CE platform, and there are starting to be lots of other emulators out there for the DC.
I'd be willing to lend my meager DC hacking skills to the effort.

I believe it CE SH4... There is someone working on it as we speak. The these older posts for info:
http://www.retrogames.com/cgi-bin/wwwthreads/showpost.pl?Board=retromamece3&Number=476&page=1&view=expanded&mode=threaded&sb=7#Post476