The question of whether or not Iron Man is going to make an appearance alongside the Guardians of the Galaxy team has been tossed around ever since the Guardians of the Galaxy movie was released last year.
Wait a minute - Iron Man? In outer space? If you're not a follower of the comic books then this might seem like a bit of a strange concept given that Tony Stark has previously been tied to the Earth in both his solo films and in the Avengers. The closest the Marvel Cinematic Universe Tony has ever come to hooking up with the Guardians was at the climax of the battle of New York back in The Avengers (2012), when he passed through the Chitari wormhole to dunk the missile right into the heart of their forces, almost sacrificing himself to end the battle.
However there is a precedent for Iron Man's outer space adventures in the source material, with Tony Stark's armour 45 - Space Armor MK III allowing him to become a member of the Marvel Now Guardians of the Galaxy (Iron Man, vol 5).
Unconfirmed rumours have persisted ever since the release of Iron Man 3 that an unfilmed post-credits sequence showed Tony receiving a distress call from outer space and flying off in the Deep Space armour which was intended to be introduced during the film itself (though this doesn't seem to fit the tone of the ending in which Tony removes his arc reactor and implies that he's giving up the suit too).
Rumours that Iron Man would make a Guardians appearance were further fuelled by tweets sent by James Gunn (director of Guardians) seemingly implying that his favourite hero (Iron Man) would be appearing in the next film. He has also confirmed that a new Guardian will be appearing, which could very well be Iron Man as he has hinted that it will be an Avenger signing up.
However, in an interview last year regarding a question of how Guardians of the Galaxy 2 would fit into Phase 3 of the MCU Gunn was reported to have said:
"I don’t feel beholden to [the MCU] at all. I think it’s really about the Guardians and what they are doing. We’re not subservient to the Avengers. Guardians 2 is not a movie that’s made to move toward [Avengers: Infinity War]. It’s something that’s made to move toward future cosmic movies, so I don’t feel that that is something that affects me that much."
Though Gunn has claimed he's not tied to the MCU, I think Guardians 2 is far more likely to include Adam Warlock (Him). Like Iron Man, Warlock has also been previously affiliated with the Guardians team and, more importantly, Warlock and his more destructive iteration, The Magus, are central to the events of Infinity Gauntlet (upon which the two upcoming Infinity War films will be loosely based).
Warlock's cocoon has been seen multiple times in Guardians of the Galaxy in the lair of The Collector (and yes, Gunn has confirmed that it was actually his cocoon) both intact...
and, during the post-credits sequence, broken apart in the background (behind Howard the Duck).
It's also seen before Guardians of the Galaxy in Thor 2: The Dark World.
Of course there's no reason that both Iron Man and Warlock couldn't be making an appearance, but introducing two such major players to this universe at this time doesn't seem to be in line with what Gunn has said about the film so far, particularly since he's said he wants one of his new Guardians to be a female character.