Later this year, Apple plans to let developers port their iPad apps to Mac computers via a new software development kit that the company will release as early as June at its annual developer conference. Developers will still need to submit separate versions of the app to Apple’s iOS and Mac App Stores, but the new kit will mean they don’t have to write the underlying software code twice.

This means major Mac OS UI overhaul and it is already going on under wraps.

By 2021, developers will be able to merge iPhone, iPad, and Mac applications into one app or what is known as a “single binary.” This means developers won’t have to submit their work to different Apple App Stores, allowing iOS apps to be downloaded directly from Mac computers

Apple will also put more restrictions in new MacOS releases on installing apps. Same as Microsoft will do in Windows.
Both companies will have big media campaigns explaining to users that only app store applications are nice and safe and all else is total horror.

Apple plans to start transitioning some Macs to its own chips as early as 2020.

Transition will be mostly done in 2021. With most Macs becoming extremely underpowered devices with horrible cooling.
They will be able to perform 10-15 minutes of benchmarks, but no more.
My source told that Apple now have special team that deals with leading benchmark authors to adopt them and avoid not very pleasant truth.

Despite the app merger plan, Apple has said it won’t combine iOS and macOS into a single operating system.

Of course, as they'll just eliminate MacOS, but it will be STILL called such.