So if you have not seen the Avengers: Age of Ultron trailer... what is wrong with you?
Bypassing all of the other awesome things in it this is what caught my eye the most. The fact that Captain America can move Mjolnir sets up something far bigger for later in the MCU. READY???
Captain America was one of the few mortals to wield the hammer. I don't think that this will play out in Avengers: Age of Ultron but i do think this will be a major plot point during Captain America: Civil War.
It looks like the hammer deems the Captain worthy and even if he cant fully wield it himself, Thor can decide to give anyone he chooses the right to wield Mjolnir.
I, for one, would love to see a hammer wielding Captain America!