This is neat!

One similar project is https://anvil.works. It's got a pure Python front end rather than HTML/CSS/JS, with a drag-and-drop designer - kinda like a modern Delphi or VB. But the client-to-server function call interface is very similar (are you using websockets too? [edit: Yes you are!]).

It's targeted at traditional web apps, rather than desktop apps, but it has an "uplink" that lets you connect local code (eg here's me building a GUI that shows text on a Raspberry Pi: https://anvil.works/blog/uplink).