Thank you. 

 If both client and relay servers run open source code that you've verified has this functionality, what is there to trust?  

 That everyone that received the event is also using a client and relay that support it. It's not about your app and your relays. It's about everybody else's.  

 So does the same thing go for burn after reading? Ie if you self host the relay, then you trust the relay, but isn't the client trust problem the same problem as someone can even shot your Snapchat?  

 Under a key delegation scheme you just publish your old nsecs after a rotation which will repudiate all non-boosted posts.