Hmm... I've always wanted something like this. Good execution. Good use of (Andy Matuschak?) Sliding Panes.

However, my opinion is that this is going to work well only in very specific situations: small teams and discussions with a high ratio of long, analytical (as opposed to synthetical) comments over multiple levels (and not just the first).

It's just too advanced for most discussions. HN/Twitter are n-level (and a thread of tweets is a kind of pre-quotes). But Most Messaging/forums don't even have a third level. And a lot of people seem to find a one-level UI like Discord and IRC enough.

Anyway, thanks for making this open source !