They could have done that at any point in the last 10 years. They're not going to. "Operating systems" are the bit that makes the hardware work for the software

They could have done that at any point in the last 10 years. They're not going to. "Operating systems" are the bit that makes the hardware work for the software, and because the hardware of "computers" is different from "portables", they'll continue to get different OS for a LONG time. Apple make mac-, i-, iPad-, tv- and watch- OS. That's five different OSs. The "bringing together" of macOS and iOS has nothing to do with unifying the OS over the hardware: it's about unifying the experience of interacting with digital representations of physical reality. Need a surface for displaying 2d media? Here's a "window" or an "app". Need to write a message to your friend? Here's a surface that accepts typed characters or your handwriting. Need to write some code? Here's a surface that accepts text and has some editing controls. Etc. What's much more likely is that they'll find some new form factor of sensors and projectors (keys, screens, pointers, loudspeakers, data i/o) that does away with "computers" and "tablets" entirely. And that'll have its own widgetOS. EDIT: punctuation.