Earlier quoted context omitted.
Neither 1 nor 2 are in fact true. Spotlight indexes all kinds of metadata, as does photos search. Adding an agent to upload data from these is easier than extending the CSAM mechanism, and the CSAM mechanism as is is not all that plausible to abuse either technically or socially given how clear Apple’s promises are.
Why should Apple's promises be taken at face value? Doubly so in a world where they can be compelled legally to break those promises and say nothing (especially in the more totalitarian countries they willingly operate in and willingly subvert some of their other privacy guarantees)? What stops Apple from altering the deal further? And if you have an answer for that, what makes you believe that 10 years in the future…
If they do, then they do. There are never any guarantees about anyone’s future behavior. However just saying ‘what stops you from becoming a thief?’, does not imply that you will become a thief.
There is no new capability other than what they have said. They already had far more general purpose mechanisms for analysing and searching your files already in the operating system.
The leap from doing spotlight indexing to searching for the keywords ‘falun gong’ or ‘proud boys’ in your files is also simple. So is the leap from searching your photos locally for ‘dogs’, to searching locally for ‘swastikas’ and reporting back when they are found.
If they decide to build some spyware, there is no need for it to be based on this. It’s a red herring.