You have secret chat that it's a great idea, no screen shot, no forward and a lot of useful features!
I wanna suggest a type of group, secret groups with same features!
In this groups, many people can talk together and they are sure that no one can forward it and no one can take a screen shot or other bad behaviors!
I know the secret chat is based on P2P but I suggest to define another version of P2P, P2 many people!!!