I think the best bet is an entirely new system from the ground up that has an open architecture that every company can equally implement that from the ground up and is as simple as possible.

This keeps getting said by people who don't understand operating systems. Even if you build something from the ground up, you still end up with an operating system very much like Linux and Windows. The choices that were made for each OS were not random. The principles of I/O, user input, graphics display, filesystems, etc, are more or less universal concepts across all OSes.

What you will accomplish is making an OS that no one will use. Linux, Windows, and macOS already fill every market that can be filled. Microsoft tried to become a third player in the mobile market and their product died pretty quickly.

Google has been trying to build Fuschia into a new OS and they've asked back their ambitions (from what I recall reading).

Yeah no thanks, a PC that can only run one program at a time? that's just a console but worse lol. almost entirely useless as a computer.