Encryption does not help, Apple still is responsible.
If Apple intends to let the user store photos in iCloud (or send by imessage) encrypted, they either have to keep the keys, so they can decrypt and scan the photos or or to keep the user from uploading incriminating content.
Apple found a third way: they will only get to reconstruct the keys if the user uploads too many pictures triggering alarms.
The US aren't the only government with a stake in that. And countries like China, Saudi, the Emirates have a lot of leverage. Financially and diplomatic. Heck, Facebook bowed to Myanmar just to get the users there.
Every cloud infrastructure holder is required for doing that. Closing an eye does not take a duty away. You must be actively pursuing that. Encryption would start flood of new laws
Tarsnap exists so either it is legal when done right or tarsnap is a walking dead and I haven't heard anything to that effect from any credible source.
