Second trailer is out. The Russo brothers, if past trailers are any indication, throw chronological continuity out the window in trailers and love leading us to conclusions that are ultimately false. This trailer hints heavily at Thor, Strange, Stark and Rogers meeting ends here; which to me indicates the truth is not this. It's human nature to try to construct meaning out of such things. In this case, don't. Wait for the movie. And simply enjoy the spectacle.
[Day later: Okay, okay. I'll succumb to human nature. I keep hoping that instead of killing Cap, Thanos sends him back in time. Cap marries Peg, and lives out a normal life in his original time. Of course, another time-rip could bring him back at any point; and that IS the point. Problem with this theory - Thanos hasn't got the Time stone in his gauntlet yet. So I suspect, with the Power stone, he'll take Cap's supersoldier serum benefits, leaving him 'normal'. He'll leave in the next film, Avengers 4. But that's a guess, just like any other.]