It turns out Joss Whedon's Avengers: Age Of Ultron may have been different if things would have worked out.
While Loki and the Grey Hulk were cut, Whedon says Spider-Man and Captain Marvel just came too late.
Empire has the following from Whedon when they questioned if the line-up in the movie was the line-up he wanted:
"Well, I wanted all those people. I said it would be great if we could just add a few more. If you guys could make a Ms. Marvel - I always say Ms. Marvel because that's when I read it. That's what it was. - If we could have a Captain Marvel there that you have made a deal for. And they talked about it. I was like 'Spider-Man, we could do that, too.' Sony had approached us during the first [Avengers] movie about a little integration. So I would have put both of them in, but neither of the deals were made. Then they were like 'we're making a Captain Marvel movie, and we've got Spider-Man as a property.' I'm like 'I've already locked my film you f-ckers. Thanks for nothing.'"
Marvel ended up announcing the Captain Marvel movie about six months ago, and Spider-Man only recently, with the new Web Crawler speculated to first appear in Captain America: Civil War prior to the new standalone Spider-Man movie in 2017.
Captain Marvel has a November 2, 2018 release with no actor yet cast for Carol Danvers.