I think FabHK is saying that Apple planned to offer iCloud users the choice of unencrypted storage with server-side scanning, or encrypted storage with client-s

I think FabHK is saying that Apple planned to offer iCloud users the choice of unencrypted storage with server-side scanning, or encrypted storage with client-side scanning. It was only meant to be for things uploaded to iCloud, but deploying such technologies for any reason creates a risk of expansion. Apple itself has other options, of course. It could offer encrypted or unencrypted storage without any kind of scanning, but has made the choice that it wants to actively check for CSAM in media stored on its servers.