Online improvements, of course. More better netcode. Priority one. Kidnap the Namco engineers, I don't care. Can't Sega slide some of that VF5FS goodness over?
Generally: let me free cancel charging moves. Fakes are cool, yo.
Character specific for characters I play/would play/hate deeply:
Helena: Any one of the 236p+k or same string ender BKO transitions should be +2 or better on block for Helena. At least even. If she's at +2 she can continue her offense relatively safely and those transitions become a serious threat, so she then has the option/desire to use her other stuff. It's not that everything ends mid punch for her, it's that everything ends mid punch and also sucks. At least if one mid punch ender is good then you have the desire to use it, people know that, and so you can mix other things up with it. Really, I think that alone would almost completely fix her problems. She should basically be the DOA Sarah (substituting BKO for Flamingo), and if she plays like that I'd play her seriously in a second. But a stance you can always, always get jabbed out of on block is pretty bullshit.
Another charge move from BKO might be useful. Say charge BKO 2k? Give a sit down stun on charged hit, could mix up with BKO 1p+k. 1p+k is all but useless as is.
BKO 6k needs to crush high or be faster or something. It seems pretty useless as is.
Maybe a high BKO entry (is there one?). Give advantage on block obviously.
Continuing on the Sarah vibe, a hit throw from BKO might be really cool. Something into a hit throw version of her back throw, maybe a high punch. It wouldn't necessarily need to give enough advantage for guaranteed damage but should keep the pressure up.
Safe on block or plus frames transition to backturned for Helena. It'd be nice to have one for Tina but I ain't greedy.
Tina:
Either a 10 frame p or make hold 3p 11 frames. Both if you feel nice about it. I have to hold crouch to get a -10 on block 12 frame mid? It's better than nothing but goddamn.
66k safe on block any distance, and/or sit down stun. I never got to play the builds where it was good, and I feel left out.
Bring back charge 46p. Mixing up with 1p+k and 46f+p is ok but it's such a bitch to space 46p to get frame advantage on the guard break.
Fix the uramawari properties on 3p+kf, it doesn't work worth a good goddamn.
Guaranteed ground throw after the hit throws (6k, k); they're basically not worth using now. Think she had one after 6k f+p in DOA 3, if memory serves.
66p+k should guard break for at least even if not better at whatever distance. It's incredibly slow and you can't follow it up at all on hit, so it's not like it would be overpowered.
Make the roll worth a damn. Something Bayman style. Maybe qcf p instead of p+k or letting you 46f+p instantly out of the roll? I'd sure use it more with those changes.
I'd love a safe 4k but that might be asking for too much.
Bayman:
More reliable juggle into 3p+k f+p ground throw. It's so awesome and yet seems to be inexplicably difficult to hit in some situations.
Differentiate 46f+p followups somehow. Maybe I'm not in the know, but I don't know why you'd pick one over the other seeing as they do the same damage. Tina has a definite reason to go with push or dropkick rather than continuing her combo throws.
Maybe a 12 frame mid, at least? Hold 3p? I don't know if he needs to be as fast as Tina but he's slooow.
Mila:
Can't think of much. She's very, very good.
11 frame 6p would be cool.
More reliable p+k to ground throws in juggles. It's difficult to time correctly sometimes.
Maybe another variation off of 3k; 3k to 4f+k would look very smooth as a combo.
Mount break options after the sprawl and side control positions get broken. Going back to even is ok but with the 2p reset there's no reason to ground throw if it doesn't go into mount or do guaranteed damage (as after unteched f+k).
Jann Lee:
Get rid of that reset nonsense (6f+k or whatever?). At least let it reset them back to neutral like Mila's reset, not to another stun state.
Lisa:
Launch into sun. Or make worth playing somehow without resorting to runaway bullshit. One of those.