Stan Lee should be added to the MCU intro because as the real-life superhero he deserves to be in it. It doesn't have to be necessarily in every upcoming movie, it is enough to get it only in the next one (Captain Marvel) or in Avengers 4.

EDIT: Just to clarify: I don't mean anything cheesy, like replacing all the clips with Stan Lee, that would be out-of-place and just bad. What I want is just a few clips in the intro that are visible enough from the rest. Like 90% of the clips could remain the same but a few clips should be replaced with Stan's old cameos.