Re: Capt. Marvel/Ms. Marvel Film? (Good idea or GREAT idea?)
Well, in terms of the reality of it being done, I don't know the rights issue.
I think if you want to rotate the Avengers Roster after A3, introducing a character like ms. marvel would be a fine choice. Could even go the Agent of Shield route if you wanted too.
I refer to this series a lot, but EMH is so good I think taking cues from some of its episodes (if they have actual tie-ins to the story/movie) isn't a bad idea. Instead of Mar-Vell transferring some power by chance, maybe have him pass on before the threat is neutralized, therefore you can get some screen time with Ms. Marvel and have her defeat whatever enemy it is they face. If doubt this would happen before A2, if it did at all though.