The problem is not building a new operating system, but app support. We have and used to have a lot alternatives, but because mainstream apps are missing no one wants to use them. They don’t have enough users, so developers won’t develop for them, egg-chicken problem. Everyone tried to solve this by android compatibility layer, but android apps will always run better on android…
I use microG since years at this point, and while most things are working, I always find some quirks, and some random apps not behaving as they should. I’m fine with that, but a non-tech guy would freak out from that. And it’s not even a completely different os, only an alternative implementation of GMS aka Play Services.
See previous and current examples, all of them was/is a good or at least usable as an os, but if you can’t use your bank’s app or whatever app you need in your daily life, you won’t switch to it. Even M$ couldn’t solve this problem, why Mr. Pei could solve it.
Edit: Obviously in the article they don’t speak about an actual OS, but one more Android skin… So Mr. Pei is not planning to solve this, they are just redefining the meaning of words, Android skins are called "OS"s in entrepreneur speak nowadays.
But they already have a “Nothing OS”: https://en.wikipedia.org/wiki/Nothing_Phone_1#Software
And they are calling that an “OS”:
Yeah, they speaking about another freaking skin…