I would be really surprised and disappointed if one of the two stingers wasn't related to Age of Ultron. It probably won't be a big four minute thing like what was shown at comic con but a shorter trailer that shows pretty much nothing like the one that was attached to First Avenger would be great. BELIEVE!!!!!
Almost all the stingers have tied into the movies they're attached to in some way or another. More often than not, they're an epilogue to the movie, not just a random tag.
Iron Man 1 = Nick Fury approaching Stark about his now-revealed superhero identity and the Avengers Initiative
Incredible Hulk = Ross talking to Stark about the Avengers Initiative (though this wasn't a post-credits scene, it served the same function, and was later elaborated on in a one-shot)
Iron Man 2 = After saying he has to leave for Nevada in the middle of the movie, we see Coulson finding Thor's hammer
Thor = Selvig getting brought in by SHIELD to work on the Teseract, where we also see Loki is still alive and interested by the relic.
Cap = Now that Cap has woken up, we go straight into an Avengers trailer which pretty much is Cap's reintegration into society.
Avengers = Thanos wants to go after the Avengers after Loki has failed him. Also Shwarma.
IM3 = Tony was actually just talking to Banner the whole time about his problem.
Thor 2 = Volstagg and Thor give the Aether to the Collector. And Thor returns to Earth and Jane.
Cap 2 = Von Strucker is not concerned now that Hydra has been revealed, because they have 'the twins". And Bucky finds out the truth of who he is.
All of these still tie to the movie at hand. We have no reason yet to assume Guadians ties in with Avengers 2 in any way. If anything, it has more to do with Avengers 3.