The real entrance cost to becoming a host in airbnb is not airbnb, its having a house. And a host will use airbnb or whatever to keep the appartment occupied. It can absolutely be commoditized, much like Lyft and Uber have. A service that posts your apt in multiple websites would make that permanent.
Today they must own the demand side: i have never seen something become so popular with no little ads (particularly in argentina, it was incredible to see it going from 0 to ubiquitous in 2 years). But demand on apartment rentals is incredibly price sensitive, demonstrated by the competition airlines have.