I was also a fan of the tekken 6 customization. I think we all know that we won't be seeing that in MK9 or any character customization for that matter, but if they did at it, the usable pieces would have to fit well in the game for specific characters. What i mean is: Glasses are available for Johnny Cage, but not for Scorpion. Scorpion could have a plethora of ninja masks, but JC would have none.
I don't mind seeing other people's customizations of already created characters, as long as they don't make them look as goofy as possible to show everyone online how 'funny they are'.