I think that Red John is Robert Kirkland as he seems very interested in Red John and is involved in the Lorelei Martins' Case. Lorelei has also said that Red John and Patrick have shook hands once. Also, the surname of the character of Robert Kirkland was, maybe, inspired by a
product of Costco - Kirkland Signature: Dried Cherries. "Cherry" is a recurring title throughout the fifth season.
This could mean that he is Red John because the fifth season focuses more on Red John and also how Jane joins the C.B.I. after wanting to see the Red John files.