Snowden’s Box – The human network behind the leak

  The institutions and endeavors we regard as ironclad — from
  parenting to politics — are actually held together with chewing
  gum and duct tape. Nothing truly works, at least not for long,
  or not in the way it’s supposed to. This reality is terrifying,
  because it exposes the precariousness of the existing order.
  But it’s also liberating, because it encourages the individual
  to act, to defy the ominous mythology of competence and control.

That turns it into a problem of securely archiving a 256bit string and escrowing it or doing some k of n thing such that it gets released if Poitras/Snowden/etc. go missing, ensuring they don't go missing. That's a much simpler problem than dealing with 8GB+ of data.

(And it only really works if you either publicize this or let NSA and any other potential adversary know about it; and you then end up with the "anyone who wants to cause trouble for NSA knocks off enough people to trigger the insurance file" problem if it's public...)

Maybe it was a test. Let's say that he in fact mailed the package anonymously. So interception would arguably have told him that he was under observation. But still, using "B Manning" seems like a confounder, even if a small one.

I'm guessing that he used different return addresses for the other two boxes. Controls for the test, as it were.