Once final Catalina is released, I plan to install and boot from an external drive, whose sole purpose will be to test how Sigil, Calibre, Alf, Kindle for Mac, etc. fare on Catalina. I will definitely report back.
I'm still hopeful that, as a last resort, it will be possible to override Catalina's Gatekeeper to allow unnotarized apps to run, even if that means they can't be signed (crazy, I know). The few articles I've seen suggest Apple does not intend to close this avenue.
That said, I plan to keep my actual Mac on High Sierra for as long as possible. The external Catalina drive will just be for experimentation
