I agree - I think only a company with pockets as deep as Google could pull off creating a brand new operating system in today's world. I'm curious to see what comes of it.
That said, to your bigger point -- I think the way to pull off a brand new OS in today's world is to write something that scratches an itch that a small-ish group of people have. Do it well enough, and it will grow into something bigger. In fact this is exactly how Linux got going. It will work again, guaranteed.
Currently, they're at around ~WinXP level support
[1]: https://reactos.org/
It was even on the verge of being a microkernel and it could run a super light weight virtualization (for the lack of a better word) system: OS personas.
It would be interesting to get Windows NT NextGen, true.