Now as for the identity of "Mr (or Mrs) Big"...
Vince McMahon: Too obvious, but not entirely without merit since this could be Vince's way of regaining control of the company. Although it's contradicted by the whole conspiracy angle starting just prior (from my perspective) to McMahon being "relieved" of duty.
Stephanie McMahon: This wouldn't make too much sense since both her and Triple H are on the same side. Although a heel turn and a kayfabe divorce/seperation could be done for the umpteenth time.
John Laurinaitis: Too obvious and I don't think WWE would put him in the top heel position.
Paul Heyman: With WWE announcing that Heyman and Lesnar have informally entered into business talks, I cannot think of a better person to play the "Mr Big" role. It's unlikely though, given that he would be favouring Punk and not working to make sure Alberto Del Rio got the title, etc.
Linda McMahon: Not likely!
The Anonymous Raw GM: Kind of a moot point really, since anyone of the previous could be the Raw GM and therefore the Raw GM could be "Mr Big" also.
I'm pretty confused as to who it could possibly be. I suppose we could argue that Triple H was behind it all the time, but that would make his actions and attitude completely contradictary. It's been established that Triple H is just as out of the loop as everyone else.