This might be overly cynical (and I'm not going to address the utility of such a USB safety net), but I can see this being used as a way to only allow <insert your multi-national tech corp. here>-approved chargers.
What I'd like to see happen is that a consortium issues certificates that sign capabilities, rather than signing identities. Essentially the charger says "the UL/USB-IF/etc. has certified me up to 18W" as opposed to "Apple built me" which seems to be the logic the industry has been using prior to USB-C.
The cynic in me thinks that having so many turing complete microcontrollers with not insignificant performance and storage is going to be the NSA and other spy agencies wet dream. You wouldn't plug a strange USB into your phone or computer but you'd probably plug a strange cable or charger around your office/house or off Amazon - and that's if you could even tell the difference at a glance.