There is still time before Avengers 2 hits theatres, but recently revealed potential spoilers suggest a pretty interesting ending for the film.
According to a theory reported on Hitfix, Avengers 2 will end with Hulk getting shot into space (a somewhat similar storyline to the Planet Hulk comic book arc).
Earlier, Mark Ruffalo had scoffed at the idea of a Planet Hulk movie, and with good reason, but that doesn't mean Marvel couldn't or wouldn't still use the idea of sending the Hulk off-planet for a future film, states an io9 report.
It looks like an interesting theory that definitely goes in line with something the folks down at Marvel Studios might have planned. Add to that, Ruffalo's tweet teasing a 'Hulk surprise' in the film.
@springrose12 Let me put it to you this way. There is a Hulk surprise that is equally delightful as when he smashed the bejesus out of Loki.
— Mark Ruffalo (@MarkRuffalo) May 21, 2014
While it remains to be seen what really transpires in Avengers 2, the idea of a subsequent film bringing Guradians along with The Avengers is definitely very cool.