The nodes are federated and you're still calling this a blockchain? What definition of the word "blockchain" are you using? Is this not more commonly called a "distributed database"?
A "blockchain", taken as a primitive, is essentially an append-only (geographically-)distributed database.
Consider: a Starcraft 1v1 ladder match is, by this definition, synchronized using a "blockchain", whose participating nodes are the two players' computers and the auditing ladder-server instance. That's not a reductio ad absurdam; that's actually what you should be picturing when you say "blockchain" generally: participant nodes, an event stream chunked into blocks, and a consensus mechanism for validating blocks.
Proof-of-work is just one consensus mechanism for blockchains. Mutually-agreed arbitration oracles (as above) is another. First-claim using a global hierarchy of signed-timestamping servers is a third. Etc.
