At the end of Avengers: Age of Ultron we saw The Hulk do the equivalent of his TV show ending, as he zoomed away in a jet to parts unknown. There were rumors that we would see him in a Planet Hulk movie in a few years, but that was shot down. We then thought that he may show up in Guardian of the Galaxy Vol. 2 with a nod to Planet Hulk, but that was shot down as well. We now have the dilemma of where we’re going to see Thor before he makes his return in the Infinity Guantlet movies, but rumor has it we now know where we’ll see him next.
According to JoBlo we’ll be seeing The Hulk make an appearance in Thor: Ragnarok, which is Thor’s next solo movie. Ragnarok isn’t a planet or new material, but a clone of Thor himself. We’ve seen The Hulk take on Thor and Iron Man, via the Hulkbuster suit, but Thor is the only one that is an actually worthy opponent. This may be how we see The Hulk make an appearance, possibly as an assistant the to the god of thunder.
In any case Marvel decided to send out this tweet coincidentally
— Marvel Entertainment (@Marvel) October 12, 2015