1. Civil War
This choice came out of one of those nerdgastic conversations I tend to have with other comic book and movie fans about the best way to bring a sprawling epic like
Civil War or Crisis on Infinite Worlds to the big-screen. The result of that conversation was the epiphany that Marvel should go all out and either commission a ten or twelve part mini-series, with the production value of Band of Brothers and The Pacific dealing with the many branches of the Civil War comic book event or a huge trilogy of movies. Just imagine it- Marvel wouldn't need to retain the same actors playing any of the superheroes involved in current "live" feature film projects due to audience familiarity with the properties and the mini-series format would allow sufficient character and subplot-line development. This excited me far too much, considering the likelihood of it happening isn't exactly huge at this point. But what a fantasy.
How Close Is It To Being Made? - Back in the early days of development for The Avengers, Joss Whedon dropped a lot of hints relating to the relationship between Captain America and Iron Man that a lot of fans thought meant that the director was setting up the Civil War storyline, and indeed you could see it happening in future Avengers movies. But the difficulty here of course is how many different parties would need to be involved, forging relationships between major studios that some might suggest as impossible, and unless we see an adapted storyline that doesn't bring in the scale or scope of the original comic, it's not going to happen any time soon.
Casting Choices: If we were to get a Civil War story arc in the current Marvel movie universe we have pretty much all of the necessary characters cast, and you can't really argue with the choices. I certainly couldn't see anyone else playing Iron Man other than Robert Downey Jr, and the studios would be incredibly stupid to build the storyline from scratch, casting aside already established dynamics and forcing themselves to offer backstories for all of the new major players. So if it was down to me, I'd do my damnedest to ensure the current iterations of the characters involved were brought into the ensemble project.
Suggested by Simon Gallagher