I think this is a bad idea. Making masteries locked means they are tied to your to character, in world, as a RPG element. World breaking for the character forget that one, then learn a new one, forget that one, learn a new one, etc, etc.
From a PvP standpoint, you'd have people metarolling to the strongest build after every balance patch.
It would bring in revenue for the game, certainly, but would have more negatives than positives.