1. There's not enough characters in the mythos yet for Civil War. If Fox/Sony agreed to a joint production cost/distribution/revenue deal that'd be great. It'd be the 8th greatest miracle the world has ever seen.

2. Hulk is simply too powerful to keep him around. He CAN'T die. And storylines where people lose their powers are so overdone already that Marvel should not consider it. Marvel needs to do something about him in the MCU (Marvel Cinematic Universe) because he is too powerful. I think a Planet Hulk movie could be awesome.

3. Why not a Secret Invasion or Infinity War storyline first while they slowly continue to introduce new characters? So far the only superheroes we have are:

1. Iron Man
2. Hulk
3. War Machine
4. Thor (and his posse)
5. Cap
6. Hawkeye
7. Black Widow
8. Ant Man
9. Falcon
10. Ant Man (forthcoming, but never mentioned or seen)
11. Stephen Strange (mentioned but never seen)
12. Guardians of the Galaxy

There's not enough earth based heroes to do a Civil War story. Civil War was probably the most ambitious of all the super story arcs that Marvel has done. It took over EVERYTHING.