At the point where you enable this feature (you wouldn't walk around with it enabled at all times because why?) the phone shows a screen asking you to get consent and the other person touches yes/no and that's it? Or would a signed form with a government seal be required?
IANAL, but from my understanding the user needs to get consent, not Apple. There would be no consent screen, apple would at most give a small dialog warning to the user that this usage is illegal (for the user). unless every participant has given consent