@zkat interesting. IMO once the instances are widely federated, anything one posts into the fediverse, it's out there propagating all over the place, and the OP has no control over what's going to happen to that post, does it get into a search database? Meta's AI tools?
The best we can is be mindful of that before hitting the Post button, on the globally federated instances.
For private and safe spaces one probably nees to limit federation to pre-approved instances.