I've got to disagree here: it has privacy implications because at Google's end they can issue a software update and now be monitoring all audio, and the T&C no doubt say they can be unilaterally varied without notification. That all means that Google think I accept Google snooping on me; of course I don't but in court Google lawyers would say I did, and them being in a position to do that is important.

Also, if Google can enable the mic at some point then it's likely that's a possibility for a third party (crackers), OR that Google could do it in response to a legal demand from a government.

There seems no good reason to me that the specification summary can't say "microphone - not in use yet, reserved for future applications"; with a sentence somewhere expanding on that explaining they want the ability to improve the device later and do shipped a mic because it could be useful to expand the products capabilities.

Some of us actually do read instruction books; it would no doubt get some column-inches in a positive way ("what changes might Google make").

Google know everything they make is going to get a tear-down and that mics are going to be discovered in short-shrift: it's ignorant to not anticipate that. In fact one really has to assume they knew this "issue" would come up.