What this guy ^ said . Years ago, when the Wii was hot and Marvel Ultimate Alliance 2 was announced, I was on an IGN board. The idea came up that the Wii version should have Nintendo characters like Link and Samus as hidden unlockables to help give the Wii version tons more value in the vein of Link being in Soul Calibur 2. Most people in the forum shitted all over the idea, talking about how Nintendo characters had no place in a Marvel game because they aren't comic book characters and aren't canon to the game. I'm like, "What the hell about this game strikes you as canon? What, is Marvel vs. Capcom canon to the comics and nobody told me?!"
Seriously, what is this sacred cow of gaming that makes people think certain characters can't cross over? Where is this hidden rulebook of gaming, or if these are unwritten rules, can we please start writing them down?
Because the idea of Marvel games is that they involve Marvel characters, duh, as well as the idea of Smash is that it involves videogame characters. Once you start allowing other stuff in, the game's core identity changes.