i don't know many of their special moves are limited.if it was an rpg and ryu was a character you would get like 6 moves to use.
also the idea of npc's would'nt fit street fighter very well since every character has his/her own story.(think about it .what if akuma was a mercenary you could hire....)
but it still is a neat idea to think about
although there is no point on putting it on dreamcast they've gone outta business