There should be a feature that can allow players to join as multiple classes to reduce the wait times in lobbies.
Upon entering a lobby, the class icons in the middle should be darkened. If a person clicks a class icon, the icon would become colored and would signify that he/she wants to play that class. If only one class is highlighted then they will play that one class. But if multiple classes are highlighted then they have the option of playing those classes. If someone joins the lobby and the current person on that class has another class highlighted and the class is open, it should move the current person to that open class.
Not only will this feature reduce wait times in lobbies, but it will act as a randomizer for those who want to try new classes or those who do not care what class they play.