I think that we have seen Red John. They wont just introduce us to some random person. Everyone loves a twist right. When Red is finally revealed it will be epic. Someone you would have thought about but then ruled out because of there innocence. Someone who is close to Jane that is a main character. Grace Van Pelt. She is the only one of the main cast that we no almost nothing about. I've even paused the TV to read her file on Red Dawn ,season 5 Episode 5, All it was was about her cousin that's a psychic, what Jane Told her about having a troubled past and about her taking part in catching a killer that enjoyed killing redheaded girls, which was from previous episodes, even though that episode was chronologically before the rest. What we do know is that she can be very manipulative when she wants. She is keeps things from others and doesn't want to admit to herself. She was the first to shoot and killed Craig O'Laughlin. The last the most cliche her bright red hair. From what I've seen my money is on her being Red John, but there are many thing that say otherwise.
Would love to here your input Thanks!