I don't think it's impossible, as far as from the film making side of it. If you have a guy like Feige in charge who has a plan, and is overlooking the whole set up, then it can most definitely work.
I think the logisitics is more of the issue.
I think it'll be much harder getting all the pieces together for future movies.
Aligning all of the actors, writers, crew, etc to do their own movies, and then do the mashup movies...I don't see how they get it all together. Big actors are attached to these movies. Look how deep the cast for this movie is.
I don't see how they'll be able to schedule in stuff when they want half of Hollywood all in one movie. These guys have other projects going on as well. Scheduling, staying in shape for their roles, their other parts...you pretty much have to BE Ironman, or whoever for the next 10 years. I don't see how this will be sustainable as the MCU expands
The Xmen is almost a universe in and of itself.