Perhaps I'm overthinking things and HTML does this naturally, but is there something for rendering that is what Swagger/OpenAPI is to APIs? Some way of specifying HTML that can be both rendered (and read back for inputs) by multiple implementations.
But as you can see, there's n+1 standards for it, and in practice none of them has a Javascript implementation good enough for productive use. So it's more a "what if?" scenario, had Angular/React/Vue not taken off.