Level 5 and Platinum Games, and SNK Playmore. Maybe Valhalla (the creators of Devil's Third) if they can make them get their shit together. And how about Atlus?
SEGA, Capcom and Koei Tecmo are too big right now, Konami a huge mess, and most bigger western developers are bound to some publisher unless they really want to stay independent. Which kind of limits the options very much...
Naturally, they could try and buy some IP, but such deals are extremly rare as the publishers prefer to sit on the IP, even if they're not using it, than allow anybody else figure out what to do with it and make money from it.







