Whilst people might make this feel like they are gutting classes more, it allows them more freedom to play with what utility other classes can have.
Say if you pug, and you dont manange to get a mage or DH, you're doing substantially less damage than someone equal gear and skill who has the buffs those classes provide. with a support spec that means they are covered. Taking this further, you could seperate them between melee classes with support roles and ranged classes with support roles. That way if support spec enters mythic + you can cater to the group you want to run with, stack melee take melee support, stack ranged take ranged support.
Im not saying its likely at all i wonder if this is a scenario they would likely think of