Hi,
For along time I thought Red John was Reede Smith ..... BUT

1. Always disregarded Partridge (DEAD NOW) and Stiles and Kirkland (DEAD NOW) as Red John - just didnt make sense it was them.

2. After Gale Bertram, Thomas McAllister and Reede Smith met as a secret law enforcement group get together with someone else in charge ... ALARM BELLS who could be giving the orders ...... Ray Haffner.

Anyway from thinking it was Reede Smith now to Ray Haffner my favourite to being Red John. 

As for what is going to happen - I agree with the previous guess .. Van Pelt/Rigsby/his infant son something nasty is going to happen to them all or just one in the final episode.