@Fosstonaut having an opt-in for allow lists is nothing special about PeerTube, and it fits well with-in the ecosystem of federation.
Not every instance is going to want to federate with *all* the other instances by default. Some are targeted by hate groups, others are not ready to handle the additional moderation load, etc.
I understand that isolation and lock-ins are part of why people flock to federated social networks instead, but let's not forget that every community has different needs.