It appears that the Guardians of the Galaxy and The Avengers may never meet. According to James Gunn, the director of Guardians, the point of the Guardians was to expand the Marvel Cinematic Universe. He stated this during an interview with Jeff Goldsmith last week according to Entertainment Weekly.
I like this idea. To use the Guardians of the Galaxy as a capsule to expand the MCU instead of trying to intertwine [The Avengers](movie:9040) into it. Possibly that was the function of the previous phase 2 of the MCU was to create the branch that would let the Guardians branch off into their own mythos. Guardians, Gunn stated "does not exist as a prequel to Avengers 3 and 4."
To have two parallel story lines going for the MCU would be great, on the one hand you'll have The Avengers and the earth-based super heroes and then on the other hand, you will have the [Guardians of the Galaxy](movie:424073) and their story lines.
The idea of the two franchises meeting is utter bliss, however, I believe to do so would constrict the whole Marvel Cinematic Universe, instead of expand. It is possible to have other characters intertwine with each franchise, but I would not expect, from a business standpoint, Marvel or Disney will put all their eggs into this basket.
However, in the spirit of the MCU, there will always be cameos and hidden Easter eggs that will give fans what they want.
So chances are, there's only a slim chance, if any, Guardians of the Galaxy will ever visit the Avengers on Earth. It could also mean that in later movies, Guardians will face foes or forces that the Avengers will face as well. Another possibility is that either franchise could set up the other to expand the MCU.
But as of now, the purpose of Guardians is to expand, and explore their universe.
SO the next question is, what do they do next, something good, something bad, or a little bit of both?