true, the "sibling chain" as you put it could allow re-orgs independent of bitcoin. but then I'm not sure what the benefit of putting all of the chain data inside bitcoin blocks would be, as opposed to just putting a hash so that nodes could simply follow a chain of headers and make sure that matches up with the chain other nodes are feeding them. can you think of what the benefits of putting all of the chain data inside bitcoin blocks would be in this case?