Mark Wahlberg has stated that he wouldn't mind taking over as Iron Man once Robert Downey Jr decides he's had enough and eventually passes on the torch. I guess, even if it did happen It wouldn't for at least quite a few more years as Robert Downey Jr has signed on for two more Avengers movies.
Wahlberg is a great talent, however I'm not sure I could ever see him fit in as Tony Stark, I guess we'll never know until it happens. Here's what Wahlberg briefly said about the matter when asked if he'd ever like to do a superhero movie.
I would like to take over the Iron Man franchise from Robert Downey, you know, it's one of those things where I kind of like playing real people, so I've never been asked.
Wahlberg at one time was briefly in the running against Chris O'donnell to star as Robin in the Blockbuster blunder Batman Forever. I guess Marky boy truly had a narrow escape with that one.