I really don't have any theories who is red john but I always hope it would be bob kirkland, but now he is dead his twin would be a great choice. I really like the way the actor  played kirkland. He made kirkland into such a unique and original character. Kirkland has all the charisma, mysterious, creepy weird vibe and I'm sure his twin wouldn't be that different. I think he made a perfect red john to me compare to other 6 suspects.