Saw this on Twitter today: The Steem Takeover and the Coming Proof-of-Stake Crisis. I like their suggestion for a hybrid of proof-of-work + proof-of-stake.

Steem actually had that for the first couple months I was here, but just one of the witness slots was reserved for miners. It was not enough to have any meaningful influence on blockchain security. And the mining algorithm was buggy. That's why they disabled it in one of those 2016 hardforks.

Dan claimed that DPoS had proven itself and it wasn't worth the effort to try to debug the problems with mining.