Chrome has had more than one JavaScript engine. They're all still Chrome to the user, and that's all that really matters. If they decide to rewrite the UI in Lisp and use Servo, it will still be Chrome in the ways that count, just like nobody cares if a game has DirectX and OpenGL versions.

Different HMDs are arguably more similar than different GPUs, and they manage to support the same software, but in the early days there were plenty of Glide-only games. That didn't work out so well. Most people will probably just use tools that optimize for any popular HMD with little enough effort that only contracts will make exclusives make sense.

Yes, because it shows Google's dedication to not leaving people out. Apple doesn't allow Google to use the real chrome rendering engine, and instead requires that every webview be webkit-based. Google would absolutely use their own if they were allowed.