Considering that they are not adding X-Men or Fantastic Four characters and probably concentrating on the MCU here are the characters I think should be in the game

Marvel:
Shuma Gorath
Carnage
Beta Ray Bill (maybe)
Blade
Punisher

Capcom:
Juri Han
Jin Saotome
Batsu Ichimonji
Ruby Heart
Leon s. Kennedy or Tyrant