@victor @jdp23 @Velveteen
I've heard from many people now that allowlist based federation is too finicky and would require too much work (much more work than blocklists).

I wonder if a basic greylist approach would cover much of this problem. Any time a server encounters a new instance that's not known, it automatically discards any media attachments, until there's been some admin review. Or maybe even some automation like, until more folks on the server follow accounts there or interact with posts.