Alright. None of us have seen Guardians of the Galaxy yet (well at least most of us have not) but I think if we piece some things together we could potentially figure out what the sequel is about. In a very recent interview, James Gunn said on the reason the Sakaraan are used in the film instead of other alien races: "...of those prominent alien races, suchas the Kree and the Skrull, I have some very specific ideas for where those races go." So obviously he and the heads of Marvel like Joss Whedon and Kevin Feige have though this out and have a plan. I think the plan goes something like this: In Avengers: Age of Ultron we know that Andy Serkins has a role, but that has yet to be specified. I'm calling it as the Super Skrull and he will appear in the mid or end credits scene -- setting the stage for Guardians of the Galaxy 2.
The Kree will already be introduced through Guardians of the Galaxy (ala Ronan.) Perhaps, after being defeated, Ronan will go back to Hala, finding it under attack by the Thanos led Skrulls. Maybe as punishment to Ronan, maybe just because Thanos wants to conqure all and found that he could not through our Accuser,so he elicits the help of the Skrulls. With Hala under attack, Ronan could go to the only group he knows could help the Krees' cause: the Guardians of the Galaxy. So Kree vs. Skrull hints the title War of Kings.
After the Guardians help Ronan and the Kree out and drive Thanos and the Skrull away, they go to Earth to attack again (because the Chitauri didn't work out) and thus sets the stage for Avengers 3.
Maybe this is all the furthest thing from the truth, but maybe -- just maybe -- this is the ground work for Phases 3 and 4. With an emphasis on the Kree, we could see a Captain Marvel movie or just a slew of Guardians of the Galaxy sequels.