In an interview with Nintendo's Charlie Scibetta, it was confirmed that players can create up to twelve user profiles.
Speaking to GameTrailers in an exclusive interview, Scibetta reiterated Nintendo's more accessible approach to linking up with other players online in Miiverse by using individual accounts on the Wii U. What wasn't know was whether there would be limitations on how many accounts can be created on each system - the answer is 12 user accounts can be stored on each Wii U.
If you have a different account from me, you might have different games featured on there, different friends and when you turn on the Wii U it can immediately go to your profile and then you'll have an experience that's tailor made for you.
Scibetta didn't touch upon whether players would or wouldn't be able to "log in" to other Wii U systems, like Microsoft's Xbox Live, at a friend's house for example.
Multiple sources, including Scibetta, have confirmed the demise of Friend Codes, yet there is word that they maybe used in some way (perhaps integrating with 3DS accounts).