Ok lets look at the 5 suspects

MC Allister: he said to PJ "iam not red john" when he showed his arm in 6x06
--------------> RJ wouldnt slander himself.

Smith: RJ would have revealed himself to Kirkland and said something about his  brother

Stiles: He said that he knows RJ, told PJ to stop being obsessed with RJ, he is too old and so on... if he would be revealed as RJ then that would have been pretty bad writing in the last seasons

So we are left with 2 possible subjects and both are dissapointing for how big the build up to RJ was.

Bertram: when he met with MC Allister and Smith, he was told by Smith that it is his responsability to keep an eye on PJ
--> RJ is an ordinary member of Tyger Tyger, by killing PJ`s wife and daughter he got the attentin of PJ so the Tyger Tyger group told him that he must take care of him and protect the Tyger Tyger Goup

Haffner: got outsmarted by PJ at the beginning of season 4, if he is RJ then he wasnt planned to be him when he was introduced

So RJ is Haffner and we just have to deal with the fact that it is bad writing or RJ is revealed to be one of many to give PJ a new goal for the next seasons -->destroying Tyger Tyger

I hope my theory is completly wrong and we get a reveal that RJ deserves