The outside of envelopes has never been particularly private, so I'm not seeing it as a policy change so much as an implementation change to support scale.
Every time I hear an argument for surveillance that boils down to “well they could just stand there and watch you do the $activity,” I lightly lose my mind.
CCTV, ALNRs, facial recognition, etc. All of these are technically “just” advanced versions of the old fashioned stake-out. But that makes all the difference in the world.
Of course this is less true in denser areas
FOREX: I applied for a new passport and the passport status says "approved, we're mailing it soon" with no tracking information. Informed Delivery shows me the package coming from Arizona and where it is in the mailstream, even if the US State Department didn't give me my tracking number.