Zap on SimpleX could be interesting, but it's probably not going to happen with the official clients. But, SimpleX Chat is an open-source project so it's certainly possible that someone could develop that down the road.  

 Zaps are identifiable. If they start using zaps, most of the privacy is gone.  

 Despite the user-free architecture, it's hard to get users to not act like users, and expect the trappings of userhood.  

 You are probably right about that!🤔