Iron Man 4 needed
So RDJr originally stated being up for an Iron Man 4. But I guess changed his mind, maybe due to being in Spider-Man Homecoming and upcoming Avengers...
Thanks to the Marvel 1 Shot we know there's a real Mandarin running the 10 Rings. I get the idea that the real Mandarin uses people to pose as him (like Ra's did in Batman Begins) which is what Killian was doing, and he in turn had Trevor Slattery for the same thing.
Captain America has dealt with Hydra... it's time for Stark to deal with the 10 Rings, going back to where it all began for him.