But that’s the thing that there kind of is not a use case and I cannot imagine there ever being one that is the only viable solution to a problem.
Fortnite could provide an option to create your skins in some sort of editor with an option to share them, sell/buy them using any currency including some fake in-game currency or even export to offline file that could be later imported back. Ownership would be tied to online account and exported file could be signed.