Earlier quoted context omitted.
Woops, you're right, thanks for the correction. I think the issue is that, as Ben Thompson pointed out, the only thing preventing them from scanning other stuff now is just policy , not capability , and now that Pandora's box is open it's going to be much more difficult to resist when a government comes to them and says "we want you to scan messages for subversive content".
Given that they obviously already have the capability to send software updates that add new on-device capability, this seems like a meaningless distinction. It’s already “just policy” preventing them from sending any conceivable software update to their phones.
However, the difference between having a feature enabled based on the value of a seemingly-unrelated user-controlled setting, versus having that feature enabled all the time... is basically zero. Additionally, extending this feature to encompass other kinds of content is a matter of data entry, not engineering. That's the policy angle.
When you don't yet have a capability, it might take a lot of work and commitment to develop it. But on the contrary, policy can be changed with the flip of a switch.