Wouldn't that require active participation of existing platforms? Seems like it'd be a tough sell.
Not really, considering the service base that makes up those platforms is trying to fragment off. They would be an easy first customer.
http://www.fastcompany.com/3057014/fed-up-with-uber-and-lyft...
Think of it as building an ad auction network for multiple websites and advertisers, rather than just trying to build an ad network for just your own website.