No character we have seen in the series is Red John.
This season they have shown us they are pretty much okay with doing flashback episodes that present us with characters that have never appeared on the show before.
All the clues they give, the shaking hands, books and rhymes, it doesn't have had to be shown on the show.
I think they will just keep writing for the character of Red John, completely unrelated to his "real identity".
If the show gets cancelled and they feel like they owe us an episode that concludes everything, they can write Red John in and build a flashback-episode around him and show us 'unseen footage' featuring Red John.
To be hones this a brilliant way to keep the series engaging, one of the worst things that happens to drama series is trying to steer it too much.
