From the UFC stand point, this is the no-brainer move in the case of a Silva loss.
Scenario 1: Weidman wins the first one, wins the second one. The chance of dismissal as a fluke win is eliminated, Weidman makes a name for himself as a marketable fighter for being the guy who dethroned the most dominant champion in UFC history
Scenario 2: Weidman wins the first, loses the second. The rubber match sells a card that will undoubtedly field 1 million+ PPV buys and obviously a sold out arena (probably MGM Grand).
Beyond the business aspect, I think that if there is any fighter in the world who can be preemptively granted an immediate rematch in the case of a loss, its Anderson Silva.