Sure, totally fair - days of continued operation would be but one metric of thousands we could use to evaluate the efficacy/security/decentralization of a block

Sure, totally fair - days of continued operation would be but one metric of thousands we could use to evaluate the efficacy/security/decentralization of a blockchain. My concern is that no matter which criteria we pick, and no matter how well PoW alternatives perform according to those criteria, miners will never vote to migrate. Bitcoin proof-of-stake would be great, but my concern applies equally to any potential eco-friendly alternatives, whether or not they've yet been invented. I work in the Ethereum ecosystem but my continued support is entirely dependent on the PoS migration... and the same factors that make me nervous about Bitcoin make me nervous for eth2. But I hope they pull it off.