Other than not having Capcom characters take up space, there's another good thing I can say about this not being another MVC. It means it's very unlikely a "character" like Sentinel will be in. If they want a robot character, there's better options like Nimrod or Bastion.
Seeing as how this is the first 4v4 tag fighter, based on Marvel characters, it should have all four of the F4. Though whether all of them make the base roster will probably depend on how big it is. And before someone brings up Ms Marvel, as gameplay videos show, she's shown to be a close-to mid range brawler. She is a grappler that wants to pull the enemy in. Reed would not and doesn’t need to play like that. He can be a long range zoner using his elasticity and technology to keep the opponent away.
This also applies to Hulk(not confirmed, but extremely likely) and Thing. If the developers want to put in a character that has similar powers as someone else in the roster, they WILL find ways to make them play differently. These guys pretty much create fighting game characters for a living.