What if...bear with me... what if there is no "Red John". First of all, they said that the unveiling of Red John would be surprising. If Bertram were to be Red John, that would not be surprisng at all, and if reed smithe or mcallister were to be red john, that would just be plain boring and uneventful. Honestly, who here is scared of reed smite. Red John is envisioned to be scary, not someone like Reede Smith. 

I think Red John is not one single person, but a whole group of people: an organization of people who go by the code word tiger tiger. They kill people and blame it on this fictional Red John character, but there is no one man actually called Red John. Thats just my two cents.

Perhaps, there used to be a real Red John, but he died a long time ago, and now this tiger group is posing as Red John. But, as of now, I dont believe Red John can be attributed to one single man.