So instead of the WoW Token working for game time, it would instead deposit the $20 into your battle.net balance. Which then could be used for anything Blizzard.
Or if you don't like the idea of WoW gold funding other Blizzard gaming hobbies then if they had a way to lock the deposited funds to only use for WoW services, mounts and pets.
Or would you rather just have the token removed altogether?
This would likely get more gold for people paying for it and let those selling gold have a bit more freedom. You can only need so much game time.