It hasn't emerged because nobody has done it. Nobody has done it because it's unbelievably hard and involves a lot of painful code of the sort that is not fun and therefore that people must be paid to write. Nobody has been paid to write it because nobody pays for dev tools and it's not in the best interest of any platform vendor to commoditize platforms.
Like any reason why Airbnb can’t open source their solution? Seems battle tested.
The thing is that many people HAVE solved this.
Some context - https://github.com/MobileNativeFoundation/discussions/discus...
(Edit to add context)
It simply is not possible to represent the realm of all possible native UIs within a common json schema. We can do it because don't need the realm of all possible UIs. We need a 20 different elements recombined and reused across all our screens.
Which is also a strength because now we can leverage our limitations into delivering a consistent experience across our app.
It can work for simple stuff. For anything more complex the underlying widgets are too different, you have to go with the lowest common denominator and the results just aren't good enough.
It's clear that in general, we are all sick of writing a bunch of bespoke code and maintaining multiple platforms, and are seeking smart layers of abstractions over native widgets. It's a tale as old as time.
What's curious is why there isn't a standard/de-facto standard (like JSON based one maybe?) for UI layouts that has emerged, with a React Native adapter for it.
We are trying to solve this problem too with the same approach (the framework isn't the product, it's just because we don't want to spend too much time building custom Mobile components for our product).
It's not like people haven't tried. Just Microsoft has probably a half dozen of these. MAUI, WPF, etc.
Again, just curious that at least one format hasn't emerged for it.