Why can't Electron be the answer? I am of the opinion that WebKit/HTML5 are the most advanced, flexible, accessible UI toolkits we've ever created. I don't think some small Rust project will be able to upset that massive undertaking which has been decades in the making. Consider also that Electron can be improved and made more efficient.
Electron is not merely a HTML5 renderer for GUIs, though; it's a whole OS abstraction layer that translates native paradigms to a platform independent format that can be scripted. An Android subsystem would be exactly that, and more, with near native performance, a shared runtime etc. And yes, even HTML5 applications that Android supports.
And it would be more than just a hack. Microsoft will have all the incentives to make it run properly, since it gives them access to a whole world of non-WinOS applications that their users will become dependent on.
