Signal is known for its cutting-edge cryptographic protocol, but this feature has the effect of throwing that out the window and replacing it with a single static key. If a device with this enabled goes through the whole advanced protocol to receive a message (double ratcheting etc), then turns around and uploads it back to Signal’s servers with a static key, isn't that a roundabout way of replacing all of signal's protocol and its forward secrecy with a static key that has no forward secrecy?
They’re calling it "opt-in," but it doesn't look like that's actually true? You can’t know whether someone you’re talking to -- who may not understand the implications -- has enabled it. In group chats, it looks like a single person turning it on eliminates signal protocol for everyone in the chat.
Based on this post, the only way to actually opt out of this is to force disappearing messages to be enabled for a time under 24 hours for every chat, which is pretty frustrating.
Signal already lags other messengers in reliability, speed, and features. The reason people use it is for its uncompromising security. Shipping something that weakens that foundation undermines the reason people use Signal.