Heh, right now we're kind of at a point where just about everything worth trying has been tried. Everything was either a novel concept that didn't quite keep its steam going (Multiversers, Movie/Anime/TV RPGs, Zombies), or based on a single franchise that didn't have enough people interested to keep it alive (Heroes, Transformers, a couple of different Star Wars ones before the current one). Or complete and utter genius that went criminally unnoticed in its time (*coughSilverAgeRPGcough*)
I do think a steam-punk RPG might be interesting, though.