That world has largely moved to "chunks", where there are multiple bundles loaded on-demand, based on e.g. user navigating to a less-used part of the web app. Going to a single file as a WebBundle would be downgrade in features.

Replacing those JS transforming kludges with a reasonable file format sounds useful, though, and allows combining JS+CSS+images in a new way.

It does sound awfully lot like HTTP Push, which as far as I know is largely unused because the idea that the server knows what the client wants hasn't really proven true.