Privacy issues aside, I assume the main reason for wanting to ship a package anonymously is because there is something inside which could get either the shipper, the receiver, or both, in trouble with the authorities.
So, now you've created an entire chain of people taking that risk! I don't see any reason for a peer to participate in such a network, but I do see a huge reason to avoid participating. Maybe I'm missing something?
To be convicted of a criminal offense, there generally has to be intent. As long as the contents of the packages are enclosed, you would not knowingly be committing a crime. Furthermore, there is no incentive to try and find out (given you would just be putting yourself at risk).
That being said, I don't see illegal activity as always being the use case for this or even the best use case. Privacy is important if you are not a criminal, too. A practical example could be that the NSA has been known to intercept computers delivered to some individuals to plant spyware in them.
http://www.pcworld.com/article/2083300/report-nsa-intercepts-computer-deliveries-to-plant-spyware.html - I suspect this is often abused, and so if the recipient is bogus, that would be increasingly impractical.
Also, I don't know what this has to do with Bitcoin Development and Technical Discussion.
If I'm right, the Death Note Incentive System (what I'm calling it) is a new way to think about how we use smart contracts. Essentially, you're curating people's incentives to perform real world multi party transactions without Oracles. Unobtrusively anonymizing the U.S.P.S. is just one simple application. I predict three more, more significant applications but I want people to review the underlying algorithm before I start talking about them to see if there are any flaws.