Warning: There are spoilers for Avengers: Age of Ultron ahead!
While it was clear where we left off with most of Earth’s Mightiest Heroes at the end of Avengers: Age of Ultron, the Hulk’s conclusion was more ambiguous. After throwing Ultron out of the Quinjet during the battle in Sokovia, the Green Goliath decided to stay in the aircraft so that he wouldn’t be able to harm anyone else. Our last shot of the Hulk was him looking at the sky as the Quinjet flew to parts unknown. Over a year before Age of Ultron was released, it was rumored that the film would see Hulk shot into space, but director Joss Whedon confirmed that, although that was never the plan, he did have a slightly different ending in mind for the Big Green Guy.
Whedon told Empire Online that it was never his intention to directly send Hulk into space, though he originally wanted the sky he viewed to be thinner so at least a few stars could be glimpsed as an indication that he could end up there. As Whedon describes it:
I wanted to leave people with the idea that, if this is the last movie, that he may have left the world behind, because I think there is something enormously poetic about that. There is also something enormously misleading about that, because they don’t plan to make Planet Hulk, as far as I know, so they were like, ‘No, just sky, no stars,’ which was less poetic, but still very beautiful.
The shot-into-space rumors that originated last year led many to believe that Marvel might be paving the way for a Planet Hulk movie, or for Hulk to appear in Guardians of the Galaxy 2. Both of these reports were eventually debunked, and Whedon’s comments tell us that he didn’t want Hulk’s fate to be as clear-cut as what happened with the other protagonists. He was listening to his inner artist and wanted to give him a poetic send-off. The only thing that really differed between his original vision and the final product was the lack of stars.
At the end of the film, Nick Fury told Natasha that the Quintet eventually crash-landed near Fiji, but Banner was nowhere to be found because the stealth technology onboard meant that it couldn’t be tracked. Marvel has been keeping silent on what their future plans are for Hulk. All we do know is that there isn’t a solo movie for him planned anytime soon, he’s expected to appear in at least one, if not both, of the Avengers: Infinity War movies, and that whatever is in store for him is "too amazing." So while most of the superheroes from Avengers: Age of Ultron have clear paths in the next couple years, we’ll just have to patient for what awaits Marvel’s green giant.