Oh, now I remember!
I intended to propose this as an official change to Phabricator.

Great idea, thanks!

Literally had that page open when I made this task and forgot about it, thanks.

I see your point in preventing room overload, too many rooms would make it a cluster of too many options.

Understood. Is it an issue that a user does not have an interface control (buttons) to Create or Join Room's when they're already in one?

Updated.