At the end of the Public Hotspot discussion, you mention that ISPs can push configurations onto privately owned routers/access points so they can connect. How is this done? My understanding is that most ISPs will assign addresses to your edge device via DHCP, but cannot configure anything beyond basic connectivity information.

The docsis standard allows cable modem operators to push configurations via TFTP. This will only work for cable modems, so if you have a distinct router/access point, then they can not do this. There are specific standards to configure the Wifi part of a modem if present. E.g. http://www.cablelabs.com/wp-content/uploads/specdocs/WR-SP-WiFi-MGMT-I06-160111-1.pdf