Great points. In fact doing classification is always a challenge, and as time goes by the line is blurred. My first idea is to place them per their appearance in history, and also the later comers (IOTA and Hashgraph) market themselves on how they are better or next-gen of first comers. Not to mention that the term “permission” can also be interpreted differently (permissioned consensus, permissioned use, permissioned governance). My attempt is just a very high-level categorisation.
Hashgraph is something very interesting: they first appear as a permissioned consensus protocol for Enterprise use and now they announced the Hedera Hashgraph which is a public ledger of permissioned governance. Let’s keep an eye how it will work when they open up for test.