panel of federated instances
Nope, can't see anything going wrong with that idea.
The great thing about federation is any instance owner can already do this, you're just asking to create an organization that decides who can federate. May as well be bluesky or reddit then.
At best you get a few major instances who together decide who can federate with them, and then those "major" instances lose traffic because people get annoyed with such nonsense and don't federate with them, their traffic slowly decreases, and eventually they become irrelevant.
Worst case: reddit.
If a few instances decide to pull this nonsense, I'll do all I can to avoid them. May make me setup my own just to ensure I don't have to deal with such authoritarians.