IRCCloud (seen below) has another perspective on compactness in a web chat client. I've been using IRC for many years, so I find myself immediately favoring this degree of compactness. Even in this half-height (567 pixels tall) window, 16 lines of messages can be viewed, and that's with a tall header for the channel topic, a line used by the "New messages" indicator, and 2 additional lines used by my long in-progress input.
Maybe what I should do is write up a request for a new feature: a "Terminal" theme (or "IRC"?) that could look something like this. The Terminal theme could also feature no userpics, emoji glyphs rendered in ASCII by default, and multimedia previews closed by default. (Or maybe those should be options separate from the theme?)
I predict IRC old-timers would love it. We're used to being able to see a lot of the past conversation at once, without having to use a large window.
Just food for thought... thanks for your consideration and effort! 
