I suspect Apple are quite happy with MacOS only running officially on Apple hardware. They tried the licensing of MacOS to other manufacturers in the 1990s and a lot of the computers released by the third parties under cut Apple on price. I doubt they will want to go down that road again especially since at the moment they can charge whatever prices they want having no competition for official MacOS running hardware.
I think they probably do envision iOS and MacOS becoming one in the future. So you can write an app once and it can be run on either iOS or MacOS but hopefully with different UI depending on if its on a phone or PC. As Microsoft showed us with Windows 8 that a one UI doesn't work for both phones and a computer.