Most developers develop for iOS nowadays, not MacOS. MacOS is increasingly an afterthought serviced by electron wrapper apps. I think it's much more likely they'll replace the Mac OS SDKs with the newer iOS equivalents.
You can now write an iOS app which runs on the desktop, and I suspect that's the direction Apple will promote - write once for iOS and it'll run anywhere, including Mac OS.
They'll obviously keep the brand Mac OS, as they do for iPad OS, but it would become the same OS as iOS once the SDKs are the same, the underlying OS is the same already (Darwin), and many frameworks are shared.