And now your messenger app needs a launcher, switcher, notification manager, search, per-app settings pages, etc. And maybe its own process model/scheduler, to prevent rogue apps from slowing down the messenger app. And apps within the messenger app now need to be cross-messenger-platform on top of being cross-webview-platform.

Let me get this straight.

- The phone OS has a shell, usually written in native code.

- The messenger app runs on top of the shell, usually written on top of some type of VM.

- The messenger app contains a web browser that renders other apps, written in js.