I think Red John is absolutely J.J. Laroche. Let's just remember the Blake's poemJ can stand for John, but there is two of J, so John John Laroche.  Tiger, Tiger... --> J.J. It is just a theory, but what made me write this theory is the second part of his name: Laroche, or La Roche, it sound french, so better say Le Rouge, which means " The Red", so basically his name means John, John, the Red ---> Tiger, tiger, burning bright. This the first prove.
The second prove, In the 5S21E Red and Itchy, the guy who has got no tongue kinda like saying "The Red John is J.J. Laroche."
It is just my idea, but Red John must be J.J Laroche, well at least, probably he is not one from the Jane's List.