I received mine today. In the package is an HTML page that lets you see your Miiverse posts page as the original Miiverse interface. If you don't see it, check other folders such as promotions (that's where mine was), spam, bin, etc. If you still don't see it, fear not, it seems everyone didn't get them at once.
A few directories of interest:
Handwritten posts: assets/user/img/pa
Your mii expressions: assets/user/img/mii
You have until December 31st 2017 to download the package.