o Thomas McAllister - The character is simply creepy. The fact that he isn't obvious would make it interesting. (See below for why I ruled out the other 6.)
BTW, I was hoping S6 would be painted on a larger canvas. Perhaps, RJ and friends could be one tentacle of an international terror/crime network. That could explain the Homeland Security and FBI's interest in RJ. Montero--Todd Johnson's friend (a known friend of RJ and serial cop killer)--was a gun-runner serving South/Central American terrorists and/or dictators. RJ's slaughter of Bosco's team presumably disrupted the investigation of a major, international drug cartel.
Why I ruled out the other 6 RJ suspects:
o Bob Kirkland - Several S5 shows provided lots of clues that Kirkland could be RJ. Disappointingly obvious if Heller chose him. He also comes across as weird and secretive more than evil.
o Gale Bertram - Bertram was not nervous (per PJ) at the mall before PJ killed Timothy Carter (S3 finale). Bertram had a plaque for bravery in his office, shown in one Strawberries and Cream episode (S3 finale). Seems unlikely were he RJ. He also has little hair--unlike the description of RJ's (blind) mistress, Rosalind Harker.
o Brett Partridge - Too obvious. Creepy, yes, but zero charisma.
o Ray Haffner - Could be, but he doesn't seem intelligent or evil enough.
o Bret Stiles - He has the charisma, intelligence and organization. But he is rather obvious. He also seems too old.
o Reede Smith - Could be, but he is too heavy to match Rosalind Harker's description. So far, he has not been portrayed as intelligent or charismatic enough to be RJ.
. and Brett Partridge seem way too obvious. The season 5 shows They would be a let-down. Bret Stiles seems too old. Ray Haffner just didn't seem to have the charisma or intelligence. And Reede Smith does not fit Rosalind Harker's physical description.