iPhones are apples leading revenue maker, but it’s closely followed by their services. Absorbing iOS into MacOS makes the most sense, they can sell devices that are iOSish only and then sell the premium dockable iPhones with MacOS. It also will help developers focus on a unified platform without alienating them with an entirely new tool suite.
I think that’s the best argument. To point for many people is the services are so good. You text someone on your phone and it shows up on your desktop. Even though macOS doesn’t make as much money it makes iOS more valuable
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.
