Not exactly a theory. Just a thought, really.

In an interview, Bruno Heller referred to whatever character is Red John as the "Keyser Söze" of The Mentalist. Anyone who know The Usual Suspects knows that Keyser Söze turned out to be Kevin Spacey‘s character who a con artist with cerebral palsy who in the end was really the sociopath, crime lord Soze himself. We saw Kevin Spacey as one person on screen the entire movie as one person and watched him "transform" during the reveal at the very end of the film. 

With that all being said, a lot of character clues will mean nothing if the character is appearing to be that different from who they really are. 

Since reading that quote from BH, I feel like there are soooooo many more red herrings out there than we are even expecting. But i do still believe in Jane saying how the answers are always obvious and right in front of us.

I love the quote from Keyser Söze himself, "The greatest trick the Devil ever pulled was convincing the world he didn't exist."

Just some food for thought! :)