Well.. since it's a spoiler thread and people have surely seen the trailer a thousand times by now i'll lay off the spoiler code.
If you watch the scene carefully you will notice that Mjolnir moves slightly when Cap tries to lift it (it even makes a tiny scratching sound on the table) and Thor notices it which leads to him losing his smug grin instantly to be replaced by astonishment.
If there was one person in that room who should be able to lift Mjolnir it would be Steve Rogers because he has all the qualities the Hammer wants its wielder to have.. honor, integrity, a warrior's heart and the skills to match it.
In the comics there were some occasions where Cap actually lifted the hammer on its own without some loopholes that makes it possible for some reason.
For the movie it could be speculated that Cap may have lifted the hammer but acted like he couldn't because he doesn't like to draw attention to himself much less be centerstage (unlike Thor who revels in the admiration of others). Maybe it was also a small clue as to what may happen later in the movie as theories go wild since Cap's Shield is shown broken it may mean the entire team is under serious pressure and Cap decides to use Mjolnir to save everybody.
We will see in a few months and i can't wait.
I know that in the comics, Cap can lift/has lifted it, which was why that scene threw me off but I'll accept that he could lift it but chose not to to not draw attention to himself.