Keeping Friend Codes is only hurting Nintendo's online ambitions. They keep emphasizing that the Miiverse eliminates the need to exchange the codes with strangers but the reality is that a lot of the people you want to add to your friends list are not strangers. With a handheld like the 3DS you might at least have it on you. Nobody wants to walk around with their Wii U FC.
Even if they are strangers like on here for instance, I still would prefer to have a name to enter and not a code.
However, if Nintendo does an advanced version of Mario Kart communities then that could be almost perfect. Someone on NeoGAF creates a GAF community, we all join of our own accord, and can then add each other from there.