I wonder if it would be impossible to carve out a set of standards of a browser (e.g. WebRender, HTML, CSS, JS Engine, ...) and then have everything outside of that be a modular plugin you can install. And make building those modules easy.

"Netflix needs a DRM module. Download this official release from <Browser Org>, <Netflix>, <Tom who really likes DRM and encoding alrogithms>".

Or am I just too naive and don't know enough about how browsers work?