Some interesting notes from Howard Oakley about Mojave, Catalina, EFI, 32-bit support and more:
Eclectic Light Co. said:Last of the Mojave
Some time in the next week or two, Apple should release macOS 10.14.6, almost certainly the last version of Mojave we’ll see, and the last macOS to run on the ‘cheesegrater’ Mac Pro. Unless something goes seriously wrong, the next macOS release after that will be Catalina, probably towards the end of September.
This update looks set to be accompanied by an EFI firmware update, perhaps for all supported models. Among other things, that should provide a firm base for the rejigging of volumes required for Catalina’s new read-only system volume, and for its other requirements. It’s easier on users if the first major release doesn’t have to include an EFI firmware update too.
... Losing all access to 32-bit apps is going to be more serious than many seem to think.