Need something for the old Skins
The solution for this seems to be getting another sword and transmuting it.
So, buy another exotic and use the Queen’s skin on it.
But I do understand your concern. They totally should.
I think they could implement a system wherein you use some sort of mystic forge recipe to unlock the skin, whatever skin you want, for your skin bank. It could even be really expensive, and people would still totally do it for this very reason.
That is a convenient idea but I have to think that would cut into the profits from T-stone sales It could be a hard sell to convince ArenaNet to give up that income.
Perhaps the ‘Skin Locker’ you suggest (that just sounds dirty for some reason) could require a T-stone to be expended to deposit a skin into a slot. That would remove the need to get some throwaway weapon to act as a holder for the skin (or finding a whole different exotic as MekubeC suggests) as well as saving bank space being used by that skin holding weapon and ArenaNet could still get sales from T-stones.