Edit: Smits has confirmed he has a cameo in Rogue One.
This speculation is based on the most brief and obscure short from the Rogue One Celebration Reel:
Is this Jimmy Smits as Bail Organa? If you're not clued up as to who he is, let's put this another way, is this Princess Leia Organa's adoptive father? He's got the same beard that Organa had in the prequels.
If so, that will be a pretty cool cameo as it was Organa who had a key role in forming the Rebel Alliance and helping out Yoda escape from the Jedi Temple in Revenge of the Sith.
It was previously thought that Bail died during A New Hope when his home planet of Alderaan was destroyed by the Death Star to show Leia how serious Tarkin was about finding the Rebel Base.
We wonder though, given Rogue One and A New Hope are so close together in time frames (and we are picking the ending of Rogue One will be Vader heading off to chase Leia's ship) is Bail Organa actually on Alderaan when it is blown up? Is he perhaps still on the Rebel base? Is he perhaps travelling to Alderaan and never quite makes it?
How cool would it be if Bail Organa was alive and well and made it through the events of A New Hope. It has never been explicitly stated in a Star Wars movie that he's dead.
If so, there could be scope for him turning up in Star Wars VIII. It's just a fan boy hope and he's better placed to be in Rogue One so we'll see how it pans out.
Truth be told, the costume looks to be more of a military leader's outfit rather than a politician.