I’d like to propose that we remove these configurations (and code):
First, I think it’s generally misguided to do this on the cache, it belongs on the origin. Secondly, Vary is a disaster, which hopefully gets addressed in the HTTP IETF WG, with Variants. Third, if you really, really want to hang yourself like this, I think you can easily do it with e.g. a header_rewrite configuration.