I just had a different usage idea for NIP-04. Instead of using it for private communication (which it is clearly had for), it could be used for teasing purposes, as an example to purposefully tease that something great is coming. As an example, a long awaited movie starts shooting, and the regisseur and an actor are talking using NIP-04, and the public only sees that they are communicating without knowing what they talk about. And a few days later, an official annoumcement is made.