Blue Luma is interesting because it actually is in the game already, all the work is done. Plus, it's the only character that gets a different version of him/herself when you face them during a special game. All other characters just swap out to someone else if you use them. (ex. Your partner for Ring Shot Challenge will be changed from Donkey Kong to Bowser if you select DK for yourself. Even Yoshi doesn't change into one of the other colors if you choose him for yourself when you'd usually face-off against him in a special game.)
On the other hand, Blue Luma doesn't have any unique equipment in the shop. It doesn't even have it's own racquet when you face it in Galaxy Rally. (It uses the original Luma's racquet, which is pretty disappointing IMO.)
I guess we'll have to wait and see if we get to use Blue Luma for ourselves. I think it would be a waste not to since it's already programmed into the game, but the fact that every QR character so far is a type of color swap (though they are technically all different beings) is a bit lame. Once White Yoshi's QR hint is posted for the US, we'll see if there is still a "Coming Soon" logo on the codes page.
Currently Playing: Virtua Fighter 5: Final Showdown (PS3), Yoshi Tennis Open (3DS), Tales of Graces f (PS3)