The third choice, after opt-in and opt-out is to force the user to choose on upgrade before they can use their device again. "Can we use an encrypted, low-resolution copy of your photos that even we ourselves can't see?"
Okay except "encrypted, low-resolution copy of your photos" is an incredibly bad explanation of how this feature works. If nobody on HN so far has managed to find an explanation that is both accurate and understandable to the average consumer, any "hey can we do this" prompt for this feature is essentially useless anyways. And, IMO, unnecessary since it is theoretically 100% cryptographically secure.
I think it's sufficiently accurate, why don't you think it is? I don't think the vector vs low-res aspect is particularly material to understanding the key fact that "even we ourselves can't see?"
