The most recent film with an intermission that I can recall was Quentin Tarantino's The Hateful Eight, though that was only included as part of the longer "Road Show" version of the film. I found it a nice break, and it was structured in such a way that it helped add to the tension of the story. You had a few extra minutes to wonder what was going to happen next before you saw the result. Certainly, such a thing could certainly happen with Avengers: Endgame. And if we're all here for over three hours, what's an extra five or ten minutes?