Below is a press release on Network ID, Youtube, and Miiverse coming to 3DS:

 A December system update for the Nintendo 
      3DS portable system will allow users to combine their Nintendo eShop 
      account balance for both Nintendo 3DS and Wii 
      U. Nintendo announced the news during a Nintendo 
      Direct video released earlier today.


 After the Nintendo 3DS system update, users can register their Nintendo 
      Network ID for Wii U on their Nintendo 3DS systems and combine Nintendo 
      eShop account balances. This will enable them to purchase Wii U software 
      using the remaining balance on their Nintendo 3DS eShop accounts, and 
      vice versa. Nintendo 3DS owners who do not own a Wii U system can also 
      create their own Nintendo Network ID for the first time.

      This system update will also mark the beginning of Miiverse support on 
      Nintendo 3DS. With a Nintendo Network ID and a wireless Internet 
      connection, users will be able to connect with players around the world 
      to share their experiences and game tips through Miiverse on Nintendo 
      3DS. For more information and notices from Nintendo about the system 
      update, visit http://www.nintendo.com/3ds/nnid.