It's not so much that ownership is a hack, or that sharing will replace ownership, but that as technology improves the transaction costs for trading property rights decreases, allowing "ownership" to be treated in a more fine-grained way than previously possible.

You can see a fairly pure instance of this situation in spectrum management (which is a common area used to study property rights because it's easy to deal with theoretically). In 1960, Ronald Coase said we should break off big chunks of spectrum and sell it off for exclusive use, just like we do with land. Transactions in those rights will help achieve efficient allocations of resources, but there is a limit at which transaction costs dominate and optimal allocations aren't reached. If you think of something very coarse-grained like frequencies for broadcast radio, you're likely to get efficient allocations via trading of property rights. If you think of something very fine-grained like allocation of frequencies to a cell phone as it travels through a busy intersection, the idea of doing micro-transactions to yield an optimal allocation becomes intractable in the face of transaction costs. But as you make the transactions cheaper, through technology, it becomes more practical to do micro-transactions.

This basic phenomenon is generalizable to pretty much any situation where you have property rights that are coarse-grained out of accounting convenience. If you can make it cheap and easy to break off little chunks of the property right and trade in them, you'll achieve a more optimal allocation of rights. That's pretty much exactly what AirBnB and FlightCar are: not sharing, but ways of breaking off a piece of a coarse property right and trading in those little pieces in a fine-grained way.