alt Hacker News>pinky promise security
You are right, though I still prefer "weak feature" as a term :) There's enough value in such things. Cryptography crowd is concentrated on omnipotent Eve breaking ciphers, and that wrench from xkcd, but I dare to claim that majority of both commercial and private leaks happen just because well-intentioned users don't have enough capacity to keep track of all the things, and proverbially think twice. Features like "unsend", or timed deletion are indeed laughable on their purely technical merits, but do wonders saving users from grave mistakes anyway.
It's hard to explain to a non technical user. Something like "We tried to delete the message, but some of the people who received your message might still have a copy." Does not sound great and is going to be hard for a non technical user to understand and hard to implement in a way that a non technical user will find satisfying.
So if I was a dev on matrix/element and this feature came across my plate I would have to weigh it against features that I know can be implemented in a way which make technical and non technical people feel satisfied and better about the application.