Specifically, sold via black lion trading for 500~1000 gems, allowing for a player to “extract” a skin from an existing item.
(This would require that the item in question has a “skin” form, and be for the express purpose of allowing players to move Halloween/Wintersday/Etc skins from PvE to sPvP)
I’m sure I’m not the only player who has used skins from before they could be converted to PvP, and would gladly pay gems to get an account-bound skin back out for the express purpose of sPvP.
Account-bound, of course, to prevent selling the skin on the trading post.