I tend to think franchise fatigue is less of a concern with movies because movies are short-enough in length that you don't feel like you just finished (or haven't finished) the predecessor when the sequel comes out.
I'd worry more about the Marvel TV products than the movies, or if the movies fail as stand-alones (like Ultron).
> or if the movies fail as stand-alones (like Ultron).
Ultron was the seventh highest grossing film in history ($1.4b gross; budget of $316 million) and the second highest grossing Marvel movie (after The Avengers).
I'm not saying it failed as a movie, but that it failed as a stand-alone movie. Imho, that's the kind of thing that would cause fatigue - too many interconnected pictures coming out that are too tangled together so viewers have no idea what they're watching unless they've perfectly kept up.
Ah, that makes more sense. I don't think that's an issue unless there are no "jumping on points", and if there's one thing Marvel is good at, it's creating artificial new starting points...
And there's lots of jumping on points coming up, with Dr Strange, Spider-Man Homecoming, Black Panther and Captain Marvel having mostly characters new to MCU and seemingly being relatively disconnected. Thor: Ragnarok might qualify as well depending on how they do it. Ant-Man and The Wasp might too - there's not much of the back story you need to catch up on.
Marvel has a large enough stable of characters to keep on churning out new standalone movies for a very long time. Though they'll need to start dipping into less well known characters, their ensemble movies and TV series will presumably let them test characters.. Then give the top performers sequels...
If they manage to get back control over e.g. X-Men and Fantastic Four too, they'll have characters to draw on for the next couple of decades at current rates...
I'd worry more about the Marvel TV products than the movies, or if the movies fail as stand-alones (like Ultron).