I don't think it is one of the men with the tattoo. Red John won't have that tattoo...his minions will. He is running the show. I think he "brands" his workers with his mark...I don't think he will have the mark himself. He regards himself to highly to share this brand...
Too much has happened that only Teresa and Patrick knew about.... I think she is the mastermind behind Red John. I think that Patrick has figured it out and that is why he told her (in the last episode) that he was going to take a break from this. She has been in his "circle" and has known all of his moves... She is Red John.