It’s very unlikely that Disney would make that reveal before the film is actually out, judging by the huge amount of speculation the trailer generated just with that point alone. Disney have enjoyed being open about their work in the past, but recently they’ve learned the importance of keeping their fans in suspense.
Most fans suspect that the figure in question was not actually Palpatine, as that would have been an obvious choice. Some publications have also brought up Darth Vader as a possible answer, but that might also be a bit too clichéd.
On the other hand, as Movie Pilot pointed out, Vader hasn’t actually been shown wearing a hood until now, which further speaks against this possibility. Either that, or we’re about to see a new chapter of the villain’s life, adding even more to his already incredibly complex personality.
We’ll have to wait until December to find out what the producers of “Rogue One” are preparing for us, but it’s starting to look like this film will be a major entry into the “Star Wars” franchise. Perhaps not as important as the main releases themselves, but it will certainly be a useful watch for those who like to learn everything possible about the lore of the series. Productions like this can often add a lot to the background of the previous films, and “Rogue One” could even reignite interest in the older movies once it’s out.