Use queue-based matchmaking to minimise wait time
Most people care only about which game type they are sitting in, not so much who else is sitting in their room. For this, queue-based matchmaking is more efficient than room-based as is currently used.
So if 6 people want to play "4 player 10 vp fast hidden bank", they are guaranteed to enter the same queue and 4 of the get put into a room that starts immediately. The remaining 2 wait in the queue for 2 more to join. With room-based matchmaking right now what could happen is they end up splitting 3-2-1 or 2-2-1-1-1-1 into separate rooms all waiting for each other. Eventually people abandon their own rooms or wait for them to fill, but this increases wait time and/or effort required for matchmaking.
Private rooms, where people actually care about the players they're sitting with could continue to exist as is or we could make changes - password entry, invites, etc but that's for a future feature request.