Let's be really frank about it - no large company is going to offer end-to-end encryption of photos because of what kind of photos might end up on their infrastructure if they do. And honestly I don't blame them
at all.
I'd just like to see Apple be more transparent with this one particular issue because it undermines so much of what they're advertising to the consumer.
A transparency label for iCloud backup showing what is and is not E2E before enabling would do. Most people (myself included) would be quite happy with photos being encrypted by an Apple-held key (I'm not worried about the police seeing my boring lunch pics, I just don't want photos of my kids being readily accessible to everyone else).
It should be made clear if they're offering E2E for some features that other settings will render it pointless is all I'm saying.