"First I want to express my disappointment if it turns out that PJ has two personas and one of those is RJ.  I also truly hope that the story line does not involve PJ and some sort of psychotic break.  It will be a travesty if the series concludes with either of these endings.
    
Just some notes and observations...

Rosalind Harker - If one were to shorten Rosalind to Rosa (Rose) one would find another writing by William Blake titled "The Sick Rose".  Google and read the poem.  It could be a hint that Red John is real (not her) as well as being Rosalind's boyfriend.
 
Many people (most) believe that in the season four finale, Red John sped by in a LVPD Police Car.  Well, when PJ is in the Limo and is greeted by RJ's voice, PJ first hears "Debonair at all costs...".  If you notice in the seen where the CBI/FBI teams drive by, the street sign reads Debonair St.  Which means that RJ may have been present in the area during the limo interaction.

In circa 1988 the Bloody Smiley Face (Watchmen Style) was quite popular in the house music scene.  Acid House music to be specific, which has often been described as hypnotic/trance-like and mind-altering music due to unique beats.
  
Also of note, the Galle Crater on the planet Mars appears in the Watchmen graphic novel.  The crater resembles a Smiley Face.  There is a Watchmen movie titled "fearful Symmetry".

There is a convicted killer known as the "Happy Face Killer".  
There is also "Smiley Face" murder theory, where alleged murders are believed to have been committed by an organized group of killers responsible for over 100 deaths.

So that got me thinking more about the name Red John.
  
Revelation 6:3-4
3 When the Lamb opened the second seal, I heard the second living creature say, “Come!”
4 Then another horse came out, a fiery red one. Its rider was given power to take peace from the earth and to make people kill each other. To him was given a large sword.  

The book of Revelation was written by John.  Thus, Red Horseman = Red John.

Also of note is the words "Its rider was given power" may indicate that RJ was given the power by someone greater than RJ.