@brion I agree with most things except on moderation, the caveat being that you need bots to do it efficiently. Modern IRCds+bots have pretty capable systems.
Matrix moderation doesn't seem up to par yet, but they have proposals in flight that are going in the right direction.
All other chat systems I've seen just use a high barrier to entry and invasive tracking stuff to discourage bad actors...which excludes people and isn't a reasonable solution.