I think my following explanation would be the most likely scenario. Capcom will release SFXTEKKEN then about three or six months later they will have the bright idea to release an updated version called Super street fighter X tekken. After the latter version has been released and received favorite reviews, Capcom will then move on to another updated version called: Super Street Fighter vs Tekken super special edition. I think this will most probably happen. They're well known for gimmicks like this. SFIV arcade edition was totally unnecessary, they should have just released two characters as DLC and that's it, but they decided to make a whole new retail version in order to make people interested in their game for a little bit longer until they announced SFXTEKKEN.
Capcom's Ono said there will never be a Super version for this one. Here's proof, http://gematsu.com/2011/11/interview-yoshinori-ono-on-street-fighter-x-tekken-fighting-games
At least he listens for now, so he won't have problems by then. I always love Street Fighter and even though Tekken is one of the games with a different fighting mechanic, I still play them both. Street Fighter is all simplicity while Tekken is in the different league in striking combinations. Both Capcom and NAMCO are just good, but friendly rivals. Either way, what Ono said should help for this discussion. He doesn't want to update that much as everyone says.
The reason they really can't release a "Super" version later is because Namco-Bandai doesn't want them to do that. They realize how bad it is for business from a reputation standpoint, and as thus, Crapcom can't release another disc-based version without their consent. At least one company is good to their customers. This obviously didn't stop Crapcom from the whole DLC fiasco, which I'm sure Namco-Bandai isn't pleased with.