““They said to me, ‘If we have you, we can do this, or Cap 3 has to be something else. It’s nice to feel needed. And at this point it’s about helping each other, too. I look at it as a competition and I go, ‘Wow, maybe if these two franchises teamed up and I can take even a lesser position, with people I like and directors I respect, maybe we can keep things bumping along.”
“It’s natural to change your views,” he says. “The main thing to me is, what sort of incident could occur, and what sort of framework could we find Tony in? The clues about where we might find him next are in Ultron. But what would it take for Tony to completely turn around everything he’s stood for? Joss brings this up all the time. It’s kind of weird that these guys would have all these throw downs all over planet Earth and yet when the movie’s over, nobody minds. What would the American government do if this were real? Wouldn’t it be interesting to see Tony doing something you wouldn’t imagine?”
The biggest question is, for Chris and for Cap, how do we bring Cap to a place where people go, ‘Man, I never thought I would see such a vast change in Steve.’ After you see Snowpiercer, you’re like, ‘I want to see a little bit of that guy.'”“
Source: ComicBookMovie