"nOOOOOOOOOOOOOOOOOOO" is my initial response, mainly because of all the negative comments I've heard about the magic bands (having to plan out your day weeks ahead of time? Only a few fastpasses a day?) Also, I hate wearing anything on my wrists, so I'd probably just shove it in a bag. To me, that's far easier to lose than a bit of paper than can slip down next to my pass in my little Fastpass/ticket holder that's a keychain on my Disney bag.
However, they seem to have already been testing/implementing the concept of the system through the disability pass. For the past eight months or so, they've been validating passes for 30-60 days for disability assistance, and then scanning them for rides. You simply tell a guest services what ride you want, they check the wait time, then scan your party's tickets. You wait half (to 3/4ths) of the wait time, then you go through the exit or through the Fastpass line, whichever is easier for the one that requires the assistance.
Before that it was a paper card, but people kept falsifying them and abusing the system. It's worked quite well, so perhaps Disneyland's might be a modification of that same system?