I don't know, this sounds like a technical solution to what is a political problem. Gmail, today, already scans your email for ads; what if congress decides that they started doing CSAM on your emails? How feasible is it for everyone to host their own email in that situation?
This also echoes the controversy with CSAM scanning in iCloud. There is no clear national consensus if the government should be allowed to invade your privacy when it comes to child abuse. Ironically, terrorists seem to have better privacy protections than a pedophile.
Personally I don't think CSAM scanning of your private data should exist, much like I think everyone should be afforded E2EE communication even if they might break the law with it. Whether we allow our privacy to be invaded in such a manner is a political/regulatory problem. A "private cloud" doesn't help if congress decides that comcast should also be allowed to MITM your SSL connection to scan every image you donwload.