[sneak]

Approximately nobody has this turned on.

It's opt-in, so approximately nobody ever will.

Everyone you iMessage with will still be putting all of your conversations and attachments and iCloud message sync keys into non-e2ee backups from their end, so turning this on won't accomplish much even if you know about it.

[marcellus23]

> Approximately nobody has this turned on.

It doesn't matter as long as the person storing screenshots in iCloud turns it on.

> Everyone you iMessage with will still be putting all of your conversations and attachments and iCloud message sync keys into non-e2ee backups from their end

Weren't we talking about storing screenshots in iCloud photos?

[BlueTemplar]

Tomorrow it might become opt-out.

But I still wouldn't trust Apple 100% : we know that they were among the companies silently cooperating with the NSA, and the potential for backdoors in their software isn't nil. (Whether you should consider this as a real threat depends on your circumstances of course.)