A blue was asked if it was a good idea for them to clear out their bank here is the blue's response.
https://twitter.com/WarcraftDevs/status ... 7653771264Transmogrification
Is it safe to sell/delete some of the transmog items? Are they already stored on account or have to wait for launch ?
Outside of quest reward items, you'll want to wait until the transmog system is available in-game before you delete any gear. (WarcraftDevs)
So if you did do so, might be a good idea to use the item restore on items that aren't quest rewards.