If Bruno Heller said a big clue was shown in the ending scene of the season premiere, I say it's this: The face Red John painted face on Lisbon is that of a CLOWN. So, Red John was a clown at the same carnival Patrick Jane used to be.

I think Red John is Brett Patridge. His voice and the voice of the masked man reciting the poem (i.e. episode with the blind woman) are exactly the same.

Too easy?