The real way around this is the Matchmaker, which will let these matches form and fill up rapidly whenever people feel like playing them.
You really think enough people play this game, that with matchmaking, a 4v4 will fill up rapidly?
of what I understand of matchmaking, I think that if someone wants to just start one on a whim, it will fill up worlds faster - though I still probably wouldn't use the term "rapidly". If people see a 3v3 with only a small handful of people in it, it'll usually get passed up in favor of a 2v2 that's half-full because it'll start faster. Right now you basically need a clan or a large group of friends to help you start one, and matchmaking doesn't have that sort of discretion.
I don't know. this is a great idea for the system we have in place right now, but it's about to change drastically, and there's not enough people in the dev app to get a good feel of how quickly these will fill. I think I want to feel out what happens when matchmaking goes in.
at that, someone correct me if I'm wrong, I think matchmaking is supposed to try to first fill the lobbies that have been open and waiting the longest. by that, if there's always a 3v3 or 4v4 open, unless a match for it just ended, it'll always try to fill those first, even if it's a slow night and there's not enough people to do so...