If what Uber and AirBnB do is lower the transaction costs of renting out an asset that is currently idled because the owner has no direct use for it, then they are doing precisely what financial intermediaries have been doing for centuries.
Improved technology has made it easier for such intermediaries to do this work over the centuries. And now we have something like Lending Tree reducing the transaction costs of potential borrowers finding FIs with funds to lend (half of the FI's inter-mediation process). And there are, of course, plenty of platforms that offer saving opportunities for households and firms with resources they'd like to add to the supply of loan-able funds.
The fungible nature of money has meant that financial inter-mediation hasn't required advanced technology to make it possible to "rent out the excess capacity" of your wealth. But such technology should be making us progressively more efficient at it.
