Re: "Ship! Come back!"
@Mark, the signal protocol used by WhatsApp requires each participant to push their group key to the new user. Whilst Signal/WhatsApp can BCC all comms to 5eyes, they are not in possession of the encryption keys used by the group conversation. If they tried to push an invite out to 5eyes, then each device could notice that the administrator has pushed an invitation to a new member.
Without weakening the security by adding a vulnerability to permit the servers to manage the session key, they cannot comply. They must either weaken security for all or refuse to comply.
Thanks very much Labor for supporting the laws of fairy math. I had held hope that you had understood what the experts were all, without exception, telling you. History will judge you poorly for supporting such a dangerous law.