FYI: Matrix has launched https://archive.matrix.org, which makes logs of world-readable Matrix channels indexable by search engines.
They made the thing opt-out; the bot (@archive:matrix.org) automatically joins out of nowhere and start archiving. You'd have to ban the bot for it to be removed, which is annoying but OK... if they didn't have a second bot ban evade and do the exact same thing right afterwards under https://staging.archive.matrix.org/ using @archive:gitter.im yesterday.
Sure, anybody can make logs of public channels, but there's a difference between "public" as in making a post about it and "public" as in reaching the front page of an established newspaper or recording conversations in a coffee shop. Or not warning people beforehand, as is the standard with e.g. IRC channels.
It sucks and they just keep making it worse while dismissing concerns or just ignoring them: https://github.com/matrix-org/matrix-public-archive/issues/47