it's going to be connected to the WiiU Miiverse, thats what Nintendo said originally, i think that the people you have on your 3DS now & the people you have on the WiiU will be combined but still split into 3DS & WiiU friends, but you will end up using the WiiU NNID for adding people to your 3DS, i also expect that you will be asked if you want to add 3DS friends to your WiiU friends & vice-versa if they have 3DS & WiiU.
people should choose their NNID carefully because eventually when the 3DS & WiiU replacements come out these will also be linked to the same account much like with Xbox Live & PSN.
the Miiverse on the 3DS will be a app just like the current ones but it will be a bit more than just the Miiverse browser that is on iphone & Android, it will have setting like the full version on the WiiU, don't forget the Miiverse is Nintendo's own IP so they can do more with the integral features on their own hardware.
out of your options it will be number 2, once the connection is made with the Miiverse on the 3DS people wanting to add you to their 3DS will add you with your NNID, if you do not have a WiiU then when you first get a 3DS if you don't have one already instead of a default FC you will be asked to set-up a NNID like the WiiU askes you to.
Edited by alan666, 27 May 2013 - 03:29 AM.