SSFV/Ultra/etc need to happen.
But, the reason why it failed to be as popular as it's predecessor is because it was half the game it's predecessor was. Quite honestly, the game is still bare bones. Except now it has cinematic mode and 6 more characters. It needed alot more. Capcom thought they could just do a few characters, stages and online and they woud be fine. Wrong!
Also, i think someone oversold Killer instinct to them. The only reason tat worked was because it was a low budget game to begin with. It was also free to start.
So, they can try to go with free. But, they should go back to what works. Make SSFV. Make an arcade mode with ending cinematics. Add at least another 6 chars and some stages. Add some new single player modes (look at guilty gear). A tag team mode would also be good. Add an omega mode. Profit!
Also, lets have advertisement reflect the story and characters. People need a reason to care.