Give it up. People have been predicting this for 15 years.
You can’t have a development machine locked down like iOS. As long as the Mac is the development machine at apple it will need to be able to run arbitrary code.
It will still run arbitrary code... Within macos...
But they'll remove support for other OS's
I mean it'd be pretty easy for Apple to just make a special version of the OS/bootloader/whatever for their internal use