I have a hard time thinking of places I really need both 0 and none. The only example that comes to mind is building room numbers, in some room search message where we wanted null to mean wildcard. In those cases, it's not hard to wrap it in a message. Probably the best argument for optionals is when you have a lot of boolean request options where null means default, but even then I prefer instead naming them such that the defaults are all false, since that's clearer anyway.

It did take some getting used to and caused some downstream changes to how we design APIs. I think we're better for it because the whole null vs 0 thing can be tedious and error-prone, but it's very opinionated.