5. It's A Licensing Nightmare
Creative liberties notwithstanding, there is no way to do justice to the Civil War story without involving a bevy of characters that are currently licensed by competing companies. Cap, Iron Man and Thor (who all play prominently in the arc) wouldn't be a problem, but securing licensing rights for the likes of Spider Man,Wolverine, The Fantastic Four and Daredevil (also important to the story) isn't bloody likely. Sony and Fox, respectively, have too much to gain by keeping a death grip on those properties. That would just be the tip of the iceberg. Attorneys would have to battle it out for some of the secondary and tertiary characters based on which comics they showed up in most frequently. Just as an example of the potential headache: Black Panther would probably be fine because he has arguably been known as either a solo act or an Avenger. His wife, Storm, would have to be left behind because she is mostly an X-Man and that is Fox property. Sorry T-Challa, gotta leave the little lady behind in the MCU. For the sake of argument, let's say all those characters can legally appear in the MCU. Who plays the parts? You can't have Andrew Garfield towing the Spider Man line for Fox while someone else is possibly upstaging him in a Civil War movie. Bring back Tobey Maguire? All new casting? This would make the Christian Bale/Ben Affleck dichotomy look like the "Dick York/Dick Sargent" switch on Bewitched.