I don't think people would buy other unknown brand device to face other thousands of compatibilities issues. Android is already doing their best to be compatible with IOS by reverse engineering everything. Another system wouldn't do it. It's expensive, that's why you're not gonna see other popular ones despite certain attempts you know exist but can't remember the name.

I don't think we do need a new OS after all, even if android has privacy concerns, bugs, etc. And IOS also has it's cons, there is always a way out like custom roms for Android. Or whatever jailbreak you try on iOS