It's not so simple.
With how crowded both DL and DHS will be when their respective SWL opens, they both need Star Tours to stay open for capacity reasons for at least the first year. On the point about Iron Man, it may seem like it makes sense because it uses the same RV, but it really doesn't. It doesn't make sense for DL because they're opening a Marvel Land across to promenade. As for DHS, Iron Man is off-limits. Disney likely wants any replacement to be cloned over at both DL and DHS.
With DL's Star Tours being in Tomorrowland, I personally have my money on a Big Hero 6 ride. I don't think it's big enough franchise to earn itself more than a new film in an old ride system and I actually think the movie would lend itself well to the ride system.