( not accusing bret stiles. Computer wouldn't let me chose anyone). Ok so I think that it is possible that we have seen red john on the show but if so he is someone none of us have thought of. I mean all of our suspects are to obvious and are just there to through us off.
As for Kirkland, he is definately not red John and is probably out for his own sort of revenge. Also all the info he got on that last episode is bogus. Jane smiled for a reason. Bret stiles is way to obvious. Mashburn too. But honestly I don't think we have seen red John yet. I think it will be someone from janes past that he hasn't seen in decades, possibly a relative.