Concur with imjared -- Uber likewise went "full circle" and started adopting more "cab company functions" once they reached the appropriate scale: "Oh, hey, we might as well make money leasing the cars too!" "Oh hey, there's money to be made in payday advances!" [1]

With that said, (per imjared) Airbnb may have some comparative advantage in the ease with which they bring this spare capacity online via a nice interface; it could become a useful platform for allowing hotels to dump extra rooms for sale, in a way that's more pleasant for users to find.

[1] Lyft lets you get paid earlier for 50 cents IIRC.