The way I've previously internalized it is CMS is bad principally because it's generic container of general generalizablity (on multiple levels, even) and the fundamentally wrong notion that signature and encryption are fully orthogonal. But generic generalizability can be ameliorated with a concerted, coordinated effort. As for S/MIME (specifically, working out how to embed CMS in MIME)... well, email and MIME make a good solution impossible from the outset, and S/MIME is probably the least bad you can do.

Encrypted email can never have a good solution simply because email is the poster child for "Why Postel's Law is a bad idea"