In a way Motion controls have always been optional in Twilight Princess. The game was designed around traditional controls and people always had the option to play it on the gamecube for that. The motion controls were sort of shoehorned in to push motion controls on the Wii but that wasn't the original design philosophy of the game.
That's why it's really easy to make them optional.
Skyward Sword is completely diffrent in that regard. The game was completely designed around the motion controls and would not work without them. They would have to redesign the whole game to make it work without motion controls, which would be more akin to taking them out entirely, not making them optional. It also would require a full-on remake instead of the remasters we have been getting so far.







