If any of you haven't listened to the Serial podcast yet, stop what you are doing...and go listen. Or maybe don't because it will consume you.

I have been reading the Fantomas books (thank you Quithat - whom I sure no longer comes here) and it made me think of an alternate and far better explanation of "He is Mar...". 

"He is many" - not that Red John is many different people (a la BA) but, rather, Red John (one person) has many personas.  "McAllister" is simply a persona.  Think of it this way....McAllister isn't Red John.  Red John created the persona of McAllister in order to hide in plain site.  
  
Still hoping that McA isn't Red John at all but the above rationale sits better with me than bringing the BA into things.