If anything that SSF4 fixes, it would hopefully be that actually implementing hit stun and block stun back into the SF series.
I do not know of any Street Fighter game has ever had as many weird cases that SF4 has had. Heck, the whole reason the game is so much a turtle-fest is because there's no block or hit stun. Street Fighter 2 didn't have this problem, Super Turbo didn't have this problem. The Alpha series didn't have this problem and the Street Fighter 3 series didn't have this problem.
It would also be nice if SSF4 actually implements a "real" combo system like 3rd Strike did. Granted, Street Fighter doesn't need a heavy combo system like Blazblue or Guilty Gear or Killer Instinct. The little land able combos found in 3rd Strike (not overly heavy execution-wise ones) worked well for the series. Street Fighter, in my opinion, works well without a heavy focus on combos. At the very least, though, they should make combos substantially easier to execute ala 3rd Strike. The ridiculousness of having to know what a Cancel, a Link and a Chain are is stupid (especially considering the fact that chains are a series of links). As I recall SF4 was supposed to be beginner/user friendly, but Blazblue, with its numerous gameplay systems is substantially more friendly than SF4 is.