Yeah in theory seeing the heroes together would be cool, but I feel like it would be jarring to see characters that are shot in a more reserved manner thrown into this for the most part brightly lit, quipathon that are the films. And I don't mean that as insult to either.
However I wouldn't mind if in The Defenders, either Stark, Fury, or Hill make a small cameo trying to recruit the Defenders at the end of the final episode. Then the Defenders can say, either in a hostile way or not, Nah we're good. We're going to fight for the everyday people. You guys can deal with the global stuff
And then maybe, if Thanos's forces attack Earth instead of the Avengers taking the fight to him, you can show them fighting off whoever in a brief cameo. Maybe.
The 2nd paragraph thing is what I really want to happen/what I think should happen