Ownership and transfer of digital assets (though I would imagine this is better and more easily solved by web2 technologies as well by cooperation among platforms).
This could take the form of lending a friend a purchased copy of a video game, Ebook, etc.
The transfer would take place on the blockchain and could be performed regardless of platform - xbox vs playstation vs steam - Apple Books vs Kindle vs Android books etc.
Though this would require agreement by these platforms who operate these services.
But again, I don't see this really happening because these platforms have no incentive to enable sharing of digital assets over selling new copies.