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.

Trends in property law and home ownership in urban areas seem to indicate that as rules and safeguards are developed for sharing more effectively, the rate of sharing increases dramatically.

Condominiums, for instance, seem like a crazy type of building if your system of land ownership is feudal, but they're a practical necessity if property value skyrockets and more population housing is needed in a dense area.

One of the main shifts in social structure occurred around the 1890s to 1920s, and was largely predicated on the difficulty associated with sharing issues in urban life, and the lack of rules to mediate that type of space sharing. Debates at the time about how to accommodate these issues were rather fierce, but mostly forgotten now. Our current laws regarding nuisance and abuse of rights are both hacks of the property system to make urban life work. Karl Polanyi's Great Transformation is a fantastic book which recounts the shift, if anyone is interested.

I'm interested in seeing what types of norms and rules would need to exist in order to fulfill the infrastructure requirement that you mention. Additionally, I wonder if certain areas of the world are already normatively primed for sharing, and whether or not they could become springboards for a more global shift.

Nailed it... "ownership turned out to be largely a hack people resorted to before they had the infrastructure to manage sharing properly"

Ownership is just an idea to align consumption with stewardship. The idea that owning stuff is "right" or "good" is just a cultural phenomenon, and not one shared by all cultures (e.g. Native Americans).

I think you could do a lot worse in trying to find a start-up idea than to ask yourself "where is there excess capacity that can be shared."

Parking, housing, office space, cooking, people-to-do-tasks, storage space, server space - this is the sharing era.