Re: IM4 in Phase 3?
At this point I'd like to see Marvel focus on other solo projects besides Iron Man - bring RDJ's Tony Stark in for Avengers movies as a big gun, but they'll have to start rotating a cast of characters.
That more individual character franchises you have, there's a bigger pool to choose from for other Avengers movies. Plus, while I know they've previously stated that they wouldn't be opposed to recasting major characters, it'd be nice for them to go away for a little while before they do so. Let's say Avengers 2 is the last film RDJ plays Stark - write the character out of storylines without killing him so you can bring back Stark 5 years down the line with a fresh face.