Three key changes have been employed in this update. Most crucially, the communities found in Miiverse can now be sorted according to a number of different criteria, such as "Virtual Console" or "Wii U Software." This is even more helpful than you'd expect as the update also increases the number of communities a player can view at once to a level that would seem unwieldy were it not for the new filters.
Nintendo has also instituted changes to your Miiverse profile page and to the communities themselves. Now, instead of seeing the total number of Yeahs you've offered other players' posts, you'll only find a number indicating how many Yeahs a post has received. Viewing posts in communities has also changed, as now Miiverse will first display posts from those who have actually played the community's game of choice, instead of displaying newest posts first, regardless of who they came from.
Miiverse is slated to hit the 3DS in December. There's no solid date on when that might happen, but a new 3DS social network delivered just prior to Christmas might help bolster Nintendo's holiday revenues.
Nintendo Wii U