Do you think the Imperial in white is Tarkin or just some Grand Admiral?
I'm hoping its a Grand Admiral. Heck, even having it be Thrawn would be pretty cool (I don't care if he is a blue alien or a white dude in the movie). The Tarkin story line can't play out all that far since he gets eliminated in E4. It might be nice having a new baddie with his own new backstory that can factor in to any other anthology movies.
I looked on IMDB and there is no mention of that character, and the guy that played Tarkin in E3 isn't listed in the credits. Maybe its Disney just being coy, or maybe IMDB just isn't built out much yet.