>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.

Sure.

In practice, in federated networks bad actors end up being blacklisted. It does not provide any "formal" guarantee, but… it tends to work fine enough. For this specific "deletion request" feature, of course it should always be seen as a convenience thing, and absolutely not about security.

As with many engineering things, it's tradeoffs all the way down. For instant messaging, a federated approach, using open protocols, offers what I value most: decentralisation, hackability, autonomy, open source. My options in this space are Matrix or XMPP. I have not attempted to self-host a matrix server, but have been very happy with my [prosody](https://prosody.im/) instance for almost a decade now.

I don't know such definition frankly. And to the best of my knowledge there are plenty of things which people call "protocols" strongly prescribing actions non-verifiable in the very sense you used. That said I'm not here for a terminological discussion. We may call it green cheese, but it's still a useful feature.

There's a difference between "I have an active adversarial actor" as a security model and "sometimes I send something I don't want to and want to delete it, the people watching are friends and acquaintances and are not deliberately preprepared to collect kompromat".

When I delete a message off Signal chat, the expectation is that the chat members are agreeing by social contract to abide by that.