Also from my reading of that, the T2 chip doesn't reboot with the laptop -- it stays powered on at all times after it first starts up. If that's really the case, a reboot won't do much except kill non-persistent things that are running on macOS itself.
So, a) a T2 hack persists until such reinstall and b) you don’t need a persistent beachhead if you’ve taken the hill and maintain persistence there. This exploit opens the door to that, and you can install keyboard intercepts via the new System Extensions Interface. Did it yesterday myself via an update to Karibiner. Notarization can be disabled by interrupting the network pathway and you can definitely disable SIP after you capture the password. In essence, T2 is the lynchpin that prevents the defeat of other aspects of macOS security.