Don't you think there will be too many superheroes to give each one a single movie? I mean Iron Man, Cap, Thor, Strange, Ant-man, Hulk, Panther, Capt. Marvel, everyone with their supporting cast and lets not forget Inhumans and GOTG. They will either drop half of them (and make lots of fans angry), or phase 4 will continue for 5 years with 3 movies every year (and oversaturation of market will happen much sooner). Or they can slow down a bit, make, say, 2 movies a year, but make it an Avengers-level events shuffling characters for each movie. And add some team-ups.
We will see - i think they will react on that, what phase 3 will bring. If all works fine, they will continue with 3 movies (expand it even to 4?).
If something does not work, maybe they will limit these characters to "team-up"-movies!?
I think we will see many characters in Captain America 3 - i expact a similar movie for phase 4...
As i see no Ant-Man 2 in phase 3, you see, they do not automatically bring a sequel! As some characters will indeed be (only) in team-up movies or in the next Avenger movie!
I think (of course

), my posted list of movies is a very good guess. I am really sure, that we will see most of the mentioned movies (if phase 3 works in total)!
But you are right. They have to find their limit soon. I do not think that it is possible to bring new faces (in solo movies) "every year"!
Not, because that would not work, but because there are already so many new faces and characters...
Therefore, phase 3 is a big test for the MCU! Maybe they even go a little bit too far with that?!
Or it just works for phase 3, but will be difficult for phase 4...
But i think, they will have a big schedule for phase 4 anyway!
For me it is quite obvious, that the MCU must still be build around heroes like Iron Man, Captain America, Thor, Hulk and The Avengers!
That are the most popular heroes - and everybody knows that. There are still so many possibilities for them - i think it would be a big failure, to limit these characters in the future to "team-up"-movies...