“But, the reality is that it takes time to add the levels to the 3DS version and it requires approval from Nintendo. I don’t expect Nintendo to have a problem with us adding the levels to the existing game (they allowed Wayforward with Mighty Switch Force), but I cannot say for certain that they will simply say yes, because I am not Nintendo. And besides, once we have added the new content to the 3DS version, we will have to resubmit the game to the ESRB and through Nintendo’s approval process, which just takes time.”
Source:
http://www.nintendonewss.com/2012/08/mutant-mudds-for-nintendo-3ds-may-get.html