The new OS that doesn’t exist yet. Linux is starting to show its age, dominated by special interest groups and with the upcoming C+Rust contention it’s a perfect breeding ground for the competitor to enter the scene. Best idea likely not to come from corporate

A new OS to replace the incumbents will only be possible in conjunction with a disruptive innovation in hardware. The device driver issue makes it effectively impossible to build a new OS for PCs, tablets, or smartphones. We don't know what the next disruptive hardware form factor will look like yet: a lot of people are betting big on AR/VR goggles but it could be something else totally unexpected.

I would say a Unix OS that can leverage existing Unix/linux tools like OSX, but more open than, and with real UX effort, native UI, not the gnome/kde, whatever stuff. Or at least something that has a Linux subsystem like windows does.

Such OS should be more secure than Linux, yet it should be able to run practically all Linux apps (and ideally Windows apps, too). It should be FLOSS with a good UI and a serious developer team. Such OS exists: https://qubes-os.org. My daily driver, can't recommend it enough.