Cain Velasquez was set to face Frank Mir in the co-main event of UFC 146 prior to Alistair Overeem screwing everything up with his testing positive for elevated testosterone. With Frank Mir called up into the main event against Junior dos Santos, Velasquez was left without an opponent.
Silva getting the call-up now leaves Roy Nelson without an opponent for the card. It's possible that Travis Browne may be given the big opportunity after wrecking Chad Griggs quickly at UFC 145, but that's just me spitballing possible replacement opponents.
I'm sure the UFC plans on trying to leave the main card as five heavyweight fights as it was a neat "gimmick" for the show.