Isn’t this what rpc/pbs/code-gen theoretically does? Markup/down sent? Then you don’t have to worry about the client or server language but settle on a subset of features somewhere.

My flow is that focusing on the data structure and methods allows the UI to be completely abstract. Not in a magic way but in a “maybe we should use cross compile this into C++ and use OpenGL if the UI becomes too complex. This is how you get AutoCad or film editing software running essentially as a Proton/video game runs.

When your app gets beyond a certain level of complexity (window composition, etc) yeah there’s ways to make it happen.