The original Red John was Partridge, of course; after season II, Bruno Heller abandoned that idea and there has been no John for quite a while (probably all the way to season V), until he finally found his candidate - someone more powerful and interesting than little old Brett was.
As to who the new John is, well... either McAllister (just because that choice would be among those unexpected), or (logically) Gale Bertram.
Note that when the seven supposed suspects were only shown in silhouettes, one - and only one - was portrayed with a prominently *blue* background. Well, consider that blue and red are the ends of the same spectrum...
(Amusingly enough, Bertram has recently said - openly - "I am MANY..." in an episode. ;)
By the way, you can vote for essentially any Red John candidate here: http://poll.pollcode.com/76818_result?v
