Most emulators don't support RAR and most of these packers aren't free or use solid archives which is a rather stupid thing if you want to use the archives directly. 7z isn't yet standarized anyway.

ClrMamePro uses a lot of lowlevel zip stuff like direct renaming without recompressing, etc. I'm not interested in porting that to rar et al ;) Maybe in a ClrMame rewrite you'll be able to add your own archive dlls....but currently there is no need.

Diskspace is cheap.

Roman Scherzer
ClrMamePro