Regarding my previous report that the “Enable default host” functionality for the AirPort Extreme and TimeCapsule was broken in firmware version 7.3.1: the issue been resolved in firmware version 7.3.2 which was released nearly a month ago (July 11th).

I was able to disable my port forwards, hop on a cellular connection and access all services as well as ping the default host. I have not yet experienced any other issues with the firmware update, but I’m not using anything beyond the WiFi & router functionalities, esp. AirDisk or printer sharing.