If you can only collect but not use it doesnt really add anything to the legacy server that didn't exist. All it does is provide incentive to play the legacy servers. There would be no moging in the vanilla servers themselves. If they add them they are most likely going to make some changes like nerfing the leveling process its never going to be pure vanilla.
Then again they may just make it so you have to pay for a server transfer to get the mog/mounts off the vanilla servers that would be a nasty way of sucking more money out of us.