Blocking Meta has more to do with not playing nice in the first place. The concern is expansion of feature sets making other Lemmy instances/clients irrelevant the way google chat did with XMPP. Google put in features not compatible with XMPP clients, while it brought a lot of users on the protocol, eventually everyone just moved to google clients. Not so much about privacy. If something is public, it is reachable.

That said, IMO the only way for that to work is if a great majority of instances block them.