I think that the writers wouldn't give us any thing that leads to red john identity.
i have a hunch.. a strong hunch that red john works for kristina frye.
I'm not counting on logical stuff of course, but there's a few like how could red john know about "Roll tide" and the fact that she knows a lot off things without being really a psychic, pretending to be dead inside when they found her and stuff.. 
the "red john person" is probably one of the seven suspects they will tell us about.  

of course it's just a hunch but i posted it so that if it was true.. i've already figure it out :3 
"sorry for bad grammar"