The Knights of Ren are still being held back, so it is entirely possible that Matt Smith’s character could be among their ranks, but the Palpatine angle is what I’d put my money on. With Ian McDiarmid in the movie, it doesn’t seem like Matt Smith will be Palpatine, but some sort of clone or apprentice would be neat. Perhaps when the next trailer arrives, we’ll get a better idea what Matt Smith’s role in this movie will be, but right now he is one of the biggest question marks.