Rumor / Datamine
Since the game’s beta hit Steam the whole 1.03 version was datamined.
Along with Hawkeye, five more heroes were datamined by their “Premium Hero Card” info:
* Captain Marvel
* Kate Bishop
* She Hulk
* Peter Parker
* War Machine
Of course nothing is confirmed so far, but I think it would be fair to say those characters will be somewhat playable in the near future. Here are my theories:
Captain Marvel comes before Hawkeye on the datamine, which feeds the theory about her being a seventh secret playable character - specially when we consider that the Krees are mentioned on the achievements for the game.
Kate Bishop comes right after Hawkeye and both have very similar play styles, just like Hulk and She Hulk as well as Iron Man and War Machine. Maybe they are considering something like the clone characters on Smash? I personally think that’s a great idea since we can expect more new characters this way.
Peter Parker is the second-to-last in the list, right before War Machine. So maybe it’s fair to expect that Kate Bishop and She Hulk comes before him? Also, it’s interesting to note that the Hero Card is named Peter Parker, and not Spider-Man. Maybe we can expect other iterations of the Hero in the future (Miles?).