Threads will want to implement post reactions to maintain parity with Facebook. Threads expands the ActivityPub spec to include reactions.
Now, every other instance will not be compatible with reactions. Users complain they cannot see reactions.
Admins have two choices now:
Refuse to implement reactions because they are not part of the spec. Users leave and join threads.
ActivityPub adds reactions to the standard, all instances must now support reactions. Meta has now started dictating the spec.
I feel the XMP fears do have some sentiment, and it’s really a matter of how the broad username interprets these issues (including the Thread users which would be family and friends).