Special Archive Nodes. you know if the archive has been altered, because the hash is passed into the new chain. Any change to the old chain would render that verification hash invalid. If there are multiple versions of the archive, only the correct one will produce the right hash.
How is a "Special Archive Node" any different than a regular node today? Since the integrity of the network depends on the existence of these "Special Archive Nodes", won't it be just as important to have them as it is to have regular nodes today?
Doesn't that mean that we effectively already have this? Aren't you essentially just renaming "full nodes" as "Special Archive Nodes" and renaming pruning nodes as "Full Nodes"?