All my non-signed apps still work on 15.1. Therefore, Gatekeeper seems to be involved here, and just setting the metadata from the command line should be enough to bypass the check.
I may even write a service to automate this so I can just right click an app and select “authorize app”. No going into settings needed.
I have to say… Roberts and Chickite come out of this looking like the people with their heads on straight.