I'll definitely have a look - I do think I saw the option in some screenshots.
If i'm misremembering, I should be able to code up the feature myself, but that wouldnt be a high prioroty rn.
EDIT: Just had a look, this does not seem to be a built-in options. I'll add this to the to do list but I've a lot of other things to get out of the way first.
You can, at the very least, see who's "online" on the chat by clicking the gears icon and making sure "Hide chatter list" is unticked.