I really hope characters aren't figurine-locked... But I'll buy them anyway.
I can almost guarantee that won't be the case. You can't limit how many people can unlock a character because nintendo can't print enough plastic figures. It would be like trying to buy a leonardo figure back in 1990. Everyone will have to settle for raph, and no one will be happy.
Well, what if if was DLC-type content that you would've been paying extra for anyway?
Supply limit for DLC? I can't imagine locking real game content behind figures for smash bros. Trophies, stickers, and MAYBE alternate costumes. It won't be anything required to 100% the game, I imagine.
Here's my idea for what they'll be used for:
MEMORY CARDS
They'll be memory cards to transfer your 'custom' character profile from game to game. You really like that custom Link moveset you created, and want to play with it at a friend's house? Transfer your Link profile to your Link NFP figure, then you can bring it to a friend's house, use it on your 3DS copy, etc.
NPF IS HOW YOU WILL LINK THE 3DS AND WII U VERSIONS OF THE GAME. That's why sakurai couldn't talk about it before.
Edit: I do like the idea of unlocking a character EARLY with NFP, but not being the only way to unlock. Sounds good to me. Really easy for tourney setups, too. Just bring the NFP stuff, unlock all characters if they aren't already, problem solved.