I disagree. If you follow the game engine analogy/thought experiment, I think there's much more that could be done.

There's a language, yes. There's also a runtime. There may be an interpreter depending on the language.

There's probably also a defined way of getting UI on to the screen in a platform independent way. There's probably also higher level concepts, maybe something that works a bit like a service worker, to use web terminology. There's likely to be a database of some sort, an app deployment system, software updates.

I'm not proposing a specific technology, but rather pointing out that there are a lot of parallels, and by realising that we're now using web technologies for shipping apps that aren't otherwise websites, maybe we could open up a lot of new potential solutions that might be even better.

There are interpreters that have offered those services for years. Hell, Didn't Visual Basic include a GUI layer 20 years ago?

I'm not arguing the utility of what your describing, just pointing out its not a new concept...

Except that you don't need to create anything new to be there. Java is already there right now. It has literally everything you listed.

Swing got an undeservedly bad reputation due to the bad default LAF. I wrote some pretty sweet stuff in Swing.

Anyway Qt is reasonably close as well, but with a compile per platform.