They should not have a character creator, but instead just improve their character designing mode. You can really do a lot, but of course there are always room for improvement. Also it would not hurt if you could dress up the characters like stuff from other IPs. It should not be too hard, give Akira Ryo's jacket, and there you go.
I also agree that there should be a story mode, but I would like it if it were set up to not be like arcade with videos, but instead an RPG mode of sorts. This could all be set through menus and work fine without upsetting the fans I think.
With that they really REALLY need to kick up the quality of the character stories. Jeffrey has been in every game because of a shark, Vanessa and Sarah lost their memories, holy shit, what is this crap? If you are going to do it all, do it at least half decent!
They absolutely NEED to design the future games to have addons in mind. I have never seen such a whiney SEGA fanbase in my life, saying stuff like just because SEGA never released Version D of VF5 that they should burn in Hell and none of their products should ever sell again. Seriously, an easy fix for this is just having addon support planned for the console releases from the start.
More females. I personally want them to make all of the characters look like 'fighters' again, and I think they can still do this while giving the girls slutty outfits. It will just change by the players tastes instead.
I think a 'Fighting Vipers' kind of gameplay mode where the players wear armor and can blast one another across the levels constantly would be recieved very well by everyone. It should be taken far less seriously than the main fighting, but given enough bulk for players to just use that and be satisfied.
Improve Quest mode to offer online options, and more online modes in general.
More features that can keep less hardcore fans for hours at a time. The RPG stuff I mentioned previously is good, but I think tons of unlockables for every little thing you can do will get players really interested in playing longer.
Better achievements that are more abundant and way easier to get.
More Sonic references I guess.