IMO it must be possible for each participant to be able of choosing the mode he knows the most. Maybe with some limitations ! for example we can decide by voting that single race is the mandatory mode (with or without weapons, all classes) and that one single race must be part of the 3 event's choice.
And i could be a way to attract some members that don't play a lot classic online modes !
As an example if an adversary challenges you in an eliminator or detonator event, he'll have to manage a tt/sl challenge