Actually, the second teaser for The Force Awakens was attached to The Avengers 2, so it's possible Disney may release the first Star Wars: Rogue One teaser prior to that (maybe during the Super Bowl?).
Slash Film has also rounded up a batch of Star Wars: Rogue One rumors which includes:
• Mads Mikkelsen‘s character is the Imperial scientist chiefly responsible for getting the final Death Star fully functional (via Making Star Wars).
Mads Mikkelsen (Galen appears to be his name in the film) is kind of the key to the film in a way. He is a scientist that took over the Geonosian Death Star project. He solved several of the flaws the Empire could not and is sort of a revered person in the Empire for his contributions. However, Mikkelsen’s character is a Robert Oppenheimer-type character. Oppenheimer helped design the atomic bomb only to say, “Now, I am become Death, the destroyer of worlds.” The guilt “Galen” feels for his contributions to the Empire become too much and he defects, attempting to make things right. In order to do this, he enlists the help of his only daughter….
• Mikkelsen's daughter may be Felicity Jones' character: teams up with a group of rebels (and bounty hunters) to destroy what her father built.
• Harry Potter's Guy Henry is believed to be playing an Imperial Officer (via Jedi News).
• Possible scene description with Bounty Hunters:
On the street, two men walk in front of the wreckage of the black-and-white X-wing fighter. It isn’t clear if they were a part of the crash or if it was just a part of their entrance. The first man has a long rifle that in spirit seems to resemble Doc Brown’s riffle from Back to the Future Part III. He has a black leather trench coat on. His mask is dull red and the visor is like a cross between Kylo Ren and and the Imperial guards from Return of the Jedi. The other man has a brown trench coat and a really big rifle with a stock that reminds me of the guns used on Hoth by the rebels in The Empire Strikes Back. If I had to guess, I would say these two are probably bounty hunters or two of the coolest extras of all time.
"Star Wars: Rogue One" has a December 16, 2016 release directed by Gareth Edwards starring Felicity Jones, Diego Luna, Ben Mendelsohn, Donnie Yen, Jiang Wen, Forest Whitaker, Mads Mikkelsen, Alan Tudyk, who plays a performance-capture character in Rogue One, and Riz Ahmed.
Rogue One tells the story of resistance fighters who have united to steal plans to the dreaded Death Star.
D23 Rogue One Teaser: