I posted earlier that my best guesses for Red John were McAllister, CBI Ron, Santa Claus and Gandhi.
After seeing next weeks promo I am taking McAllister's name off the list 100%. No way they would give RJ identity away in a 30 second promo.
My thoughts say that the timeline wouldn't fit. If McAllister is RJ and that is him walking into the church at the beginning of next weeks episode and he gets shot, it rules him out completely. We see McAllister fleeing but we don't see him get away. If he does get away, why would he agree to meet Jane (as said later in the promo) after already being shot and facing certain death.

I just watched a video on Youtube of an editor for a TV blog. He posted a video of his live reactions to next weeks episode which contains absolutely 0 spoilers.
Here's the video for those interested: "youtube.com / watch?v=vWYpReqi678" Remove spaces.

At one point in the video his jaw literally drops and he goes a little insane. If this is the moment RJ is revealed he's reacting to, I assume that RJ must be either someone dead (maybe from the list) or someone out of nowhere (eg. Ron or the bald guy in my picture). But obviously it doesn't end up being Bertram and I doubt McAllister.

Gandhi it is.