I actually think that Jin is more suited to be a rival to Ryu than Kazuya ... dunno but thats just h ow i see it. Too bad Jin doesn't have a "ken" ... maybe hworang, but it just seems more fitting for him to be with steve :S
I think Kazuya might be a great rival to Akuma because both of them have that same undying thurst for power and they are just plain assholes, so it fits i guess
Kunimitsu vs Ibuki should be made in this game IMHO, Maybe if kunitmitsu was tagged with zafina, and Ibuki with Rose, the rivalry could be more intense.
Chun li ... i don't know who actually fits to be her rival, but in my head, Nina or Julia is a better fit than Asuka or even Lili.
Karin Vs Lili is what should happen ! Damn you Ono for not seeing the OBVIOUS, sakura/karin vs asuka/lili is just so damn obvious ... and its more appropriate.