The director of Super Mario 3D Land spoke at GDC today and opened his talk with a brief look at the ideas that could have been. From different "forms" to new ways of beating enemies, some of these always have the potential of turning up in sequels but, for the most part, I'm hoping that they don't.
Take for instance, the ability to transform Peach's face into the face of your girlfriend using the 3DS cameras. I'm not sure that would be flattering, but part of me wants to try it. If that doesn't do it for you, how about a cockroach enemy that would start by crawling down from the top screen and you would have to close the 3DS on it to kill it?
These are minor things that would be neat features if included, but nothing game changing. Factor in "Huge Mario" and "Long Mario" and you've got yourself a whole new set of levels. Huge Mario would have filled the screen in such a way that you'd have been unable to see anything but his legs. Long Mario would have been able to stretch his limbs. Ah, the things that could have been.
Source: Joystiq