- Captain Marvel
- Spider-Man
- Doctor Strange
- T'Challa
- Ant Man
- Wasp
These six will be at the forefront of the next Avengers film (I suspect), with Bucky and Sam jumping in with a cameo scene. I doubt we'll see Rhodes. Wanda and Vision aren't likely going to feature either; I figure their development (and Visions restoration) will keep them occupied in a secluded part of the world. I think we've seen the last of Valkyrie too.
I'm not seeing Thor 4 either, though depending what happens in Guardians 3, I can see Thor making a return in another MCU film; possibly Avengers 6 or something? Spider-Man 4 is open to me; they obviously cast young for a reason, and with it not being a direct Marvel property, it's possible Sony would desire a second trilogy with Tom, and if that's the case, we'll probably get it; all whilst introducing other Spider-People along the way.
Short of newcomers too, Captain Marvel, Doctor Strange and Black Panther will be the next trio of films to get a sequel. I don't know what (or where) they can currently go with Ant Man 3, though I have no doubt it'll come at some point, though it wouldn't surprise me if it's more Civil War in tone (in that it's less about Scott and Hope, and more about a small ensemble of characters).