Like all things I believe this will sort it's self out...maybe their will be a few games of all new gods...but when you join a room the the creator makes the rules if you dont like them start your own game/room.
Enough said
That doesn't answer anything; yes the creator sets the rules, and you know what those rules usually are no doubles and no tripples. You still had have to decide who gets to use which demigod and if one party deams it unfair and leaves. Than you have to wait for another person, ontop of that chances are you will have the same comflict with the new arrival. This will lead to mroe than one person leaving this time and a game that should have and could have doesn't get started.
Most players don't regulate who can't use what demigod,and I have only really seen this happen when I want to use QoT. Even than it was rarely done.