This opt-in, because of sneak's law ("users can not and will not securely manage{generate, backup, authenticate} key material")[1]. Apple knows that enabling this by default would be a disaster. This means most people will not ever even know the feature exists, and few will turn it on.
This means that iMessage as a platform is still backdoored, because most people you iMessage with will be escrowing their endpoint iMessage keys to Apple in their effectively unencrypted iCloud Backups.
Apple (and the FBI/DHS/CIA/NSA soup bois without a warrant) will still be able to read everyone's iMessages in real-time.
Everyone wins. Spies keep spying, Apple gets to trot out the e2ee marketing flag.
Meanwhile, there is nothing to indicate that they don't intend to continue the rollout of their clientside photo scanning software that they previously announced.
This means that iMessage as a platform is still backdoored, because most people you iMessage with will be escrowing their endpoint iMessage keys to Apple in their effectively unencrypted iCloud Backups.
Apple (and the FBI/DHS/CIA/NSA soup bois without a warrant) will still be able to read everyone's iMessages in real-time.
Everyone wins. Spies keep spying, Apple gets to trot out the e2ee marketing flag.
Meanwhile, there is nothing to indicate that they don't intend to continue the rollout of their clientside photo scanning software that they previously announced.
[1]: https://youtu.be/9k4GP3Evh9c