I believe that they will go with the obvious suspect Brett Partridge.  I say obvious because most die hard fans of the show (anybody that frequents this website) would know right off the bat that there are many signs that point to him. 

That doesn't mean that the casual viewer that watches every week but doesn't keep up with all the hints will feel it's a cop out.  Most will be shocked and pleasantly surprised that someone who's been in important episodes briefly ended up being Red John. 

I don't think the show will end with his death or capture either.  Jane will either die by his hands or it will be revealed that Brett Stiles created Red John somehow.  This will push Jane's vengeance to a new level and he will be motivated to take Brett Stiles down after he's finished with Red John.