Has a consensus algorithm where temporary authorities are fairly “elected” via PoW been discussed?
I’ve since found several related concepts in research papers or coin protocol proposals:


Bitcoin-NG separates leader election (key block) and the following “election term” (epoch), in which microblocks are freely added by the leader.
Tendermint (and, before it, Hyperledger) uses BFT consensus (but with PoS as the basis for elections).
Building upon the previous, ByzCoin elects leaders via PoW and uses PBFT to agree on the microblocks.


The article The Road to Scalable Blockchain Designs gives a good intro to and context for ByzCoin. Exploring the citation graph of the ByzCoin paper leads to further similar work at ETHZ and Cornell as “hybrid consensus” or a “strongly consistent” blockchain.

None of these use the energy-savings aspect that motivated me; instead they all aim at improving throughput and/or transaction verification time. But the “PoW leader election + BFT consensus” concept seems to be pretty actively researched.