Keep the friend codes in some form. For example: I don't want unwanted folks adding me randomly. I'll hand out my code to people I WANT to add, so that way, I know for sure who I'm adding and because it's someone with a unique code and not someone who has a similar name... or something.
Sucks that they'll be gone, but I like friend codes. And keeping them in some form would be cool. I'll have to put my account on special lockdown.
Don't like random people trying to add me.
Oh, and 3DS codes beat Wii Codes :3
Nintendo did a good job with only one FC. Then again, I like having multiple friend lists because my Brawl list got full by adding people on All Is Brawl to play matches and I like keeping most as they are competetive- something I doubt people currently on my 3DS list are (all from NL).
That's the real pro of having multiple fcs for games. But that's about it lol