My only concern with Fedor vs Brock is that Fedor comes in at about 220lbs and Brock come in around 280lbs. Brock is the top of a new breed of super-heavies. Now GSP is one of the best, if not the best P4P fighters on the planet, but, he'd get his arse handed to him by an average heavyweight due to the size advantage - once the heavy gets ontop of you and is fairly savvy to submission defence, then it's curtains.
I'm concerned that if Brock vs Fedor ever happened, Brock would charge him, put him on his back and just lie on him for 3-5 rounds and win a decision, or even worse ground out a TKO. When Brock is not a talented fighter what so ever, if he was 50lbs lighter he would be cannon fodder.