I had an idea on speech: "f fronting" and "v fronting" (its voiced counterpart). The idea is to make these sounds into labial fricatives. This is "th fronting to the next level". Could a speaker notice that I was talking differently?
Sound change in IPA notation:
/f/ -> /ɸ/ and /v/ -> /β/
Note: this is not (usually) someone trying to pronounce it because this is like a native language. It is generally a thought experiment.