Civil War is way too big of a story to be crammed into one movie. And Marvel’s moving steadily towards the two part Infinity Wars conclusion to Phase 3.
So I’m guessing in the Cap Civil War movie they stick to the concept from the comics and condense it down considerably so it doesn’t require Spidey.
At the same time the targets of the “Registration Act” can be the Inhumans, which were just introduced in Agents of SHIELD and may play a role (Scarlett Witch and Quicksilver possibly being Inhumans) in Age of Ultron.
I could see that being done with the inhumans. I figured it would be a multi-movie set later down the line.
I was personally hoping they would get there if for no other reason than to see Thor wipe the smirk off Starks face - that was a bad ass scene that I’ve reread with enjoyment multiple times. It would translate to a movie scene so well too.