Okay so contracts won't last forever. Ruffalo, Downey Jr, Hemsworth and Evans' contracts expiry dates are very well known and Renner/Johannson's are questionable. That said, we have a lot of new blood and hints at what the roster could look like going into Phase 4 and onwards.
You must be registered for see images
Predicted Roster:
Ms. Marvel (Brie Larson)
Has the potential to become the new leader / mascot of the series. Not hugely iconic but a very big-scale authority-taking character. Is currently the leader of the new Avengers Civil War II split.
Bucky Barnes / Captain America (Sebastian Stan)
Stan has a bigger contract with Marvel than any other actor. No prizes for guessing what mantle he'll take up with Evans leaves the franchise.
Dr Strange (Benedict Cumberbatch)
Star status and mystical representative. Depending on how well received his solo film is, could be a huge or small role.
Black Panther (Chadwick Boseman)
Avengers staple from now on. Awesome character that is here to stay hopefully.
Antman (Paul Rudd)
Another Avengers movie without Antman is a sad thought.
Spiderman (Tom Holland)
Will take his time to join the Avengers ranks but is an obvious must.
Scarlet Witch (Elizabeth Olsen)
Young preppy Avenger has more to bring to the series. Unfortunately for her, it's mostly misery and destruction.
POSSIBLE:
Vision (Paul Bettany)
May die in the result of Infinity War but another long-running Avenger. May live to marry Wanda.
Falcon (Anthony Mackie)
Bucky's inclusion means he won't become the Cap which means that he'll either be killed off (unlikely in Disney) or drop the Avengers with the departure/death of Steve Rogers. Maybe he'll just stick around.
UNLIKELY:
>Guardians
Unlikely to join the Earth world outside of crossover event movies. Still cool.
>Black Widow (Scarlett Johannson)
Contract has 'morphed' over the years. Who's to tell how much more it can change?
>Fantastic Four
Thought that the current deal being made with Fox is a chance for them to lend out the character akin to Sony/Spiderman deal. Just a hopeful thought.
---
Any other suggestions? Anybody you want to join the team they haven't introduced yet?