We already have self destructing notes (NIP-40 - Expiration Timestamp) but NOS Social is the only client (AFAIK) that uses it. 

We just need better support in apps. Would be cool to visualize them with some kind of icon/countdown as well.

One concern is that reposts (which copy the note's content) could be used to circumvent the expiration. 

CC  @juan 

 Would the repost of a note also have an expiration? 

 I couldn’t find any mention of that in the spec. I would expect apps currently don’t carry forward the expiration for reposts.

Also note: expiration is optional, I.e. it SHOULD be considered but it is never a guarantee.