You're "downloading an app" anyway, even if it's JavaScript running in a browser. How do you think the client-side code gets to the client‽

But yes, I think we need a new version of something like Java Web Start, except with the ability to steam parts of itself as-needed instead of having to download the entire .jar before being able to run. If you're going to have an app, have an app that has proper libraries for the UI etc. instead of hacking everything on top of a whole bunch of DOM cruft!

I guess WebAssembly is a step in the right direction, but it's still too tied to the document viewer known as a "web browser," for no good reason.