Add a feature where if enough people join (right as the game should start) the site plays a relatively loud sound effect and people have to click that they are there. It should have at least a minute long timer where people can come back from a bathroom break or whatnot. If people don't ready up, kick them from the group and let others join. (They do this for Team Fortress 2 LFG's, works like a charm) https://tf2center.com/lobbies