Guardians of the Galaxy Vol 3
Almost guaranteed to fill one of the slots after the huge success of the first film and with Vol 2 on it's way.
Spider-Man 2
Again, very likely. Spider-Man films make money and Marvel will be keen to bring a flagship character further into the MCU. However I wouldn't be suprised if this takes the form of a Sinister Six film - especially if Suicide Squad does well for DC.
Dr Strange 2
Every solo film except Hulk has got a sequel so far so presumably this will be no exception.
Infinity War Part 3
aka Avengers 5! Probably not but would be amazing if this was the third mystery film and they managed to keep it secret until we see a shock cliffhanger in Infinity War Part 2.
Black Panther 2
It might be too early for this after having BP in Civil War, his solo film and presumably at least one Infinity War film.
Vison & Scarlet Witch
Neither could support a solo film but a Team Up in the style of 'Ant-Man and the Wasp' looking at their unique relationship could be interesting. Of course they may not both survive Infinity War...
West Coast Avengers
Probably not quite enough characters to support two Avengers teams just yet.
The Defenders
After years of building on Netflix and perhaps a role in Infinity War could the team get a movie outing? Or maybe a Heroes for Hire film is on the cards. Depends what deal Marvel has with Netflix - they may want to keep them on the small screen. Also the darker tone could be hard to translate to a movie.
Fantastic Four
Could Fox come to a Spider-Man/Sony style deal?
Hulk
Legal rights with Paramount make this unlikely but a version of Planet Hulk could be set up in Infinity War, and perhaps World War Hulk would be a good Avengers film. Failing that the Leader, Abomination and Ross are still around...
New Captain America
If Steve is dead or retired by this time then Bucky could be ready to pick up the shield. Like Winter Soldier and Civil War this could also bring in lots of other characters, and maybe the return of Red Skull.
Iron Man 4
It's assumed that Marvel will stop at trilogies for it's solo characters (and I hope that is the case) but we know the real Mandarin is still out there.
Black Widow
I think the ship has sailed on this but the fans still seem to want it - Widow and Hawkeye on a black ops mission perhaps?
Inhumans/GotG/Captain Marvel spin-off
With lots of cosmic characters and concepts being introduced maybe the groundwork can be laid for a spin-off film - Nova, Adam Warlock etc?
Moon Knight
There was a vague mention in the Winter Soldier after all...
Runaways
They've had a script knocking around for years now...
Blade
They have the rights back although it might be tricky to work vampires into the MCU.
Namor
I guess it's possible, maybe if Aquaman does well.
Cloak & Dagger
I see this more as a Netflix show but who knows?