Apparently, long-limbed Mario was only a joke
Remember when Super Mario 3D Land director Koichi Hayashida discussed some ideas that were never used in the game? There was "Pro Skater Mario," which was very reminiscent of Super Mario 64's Koopa shell-riding. There was also the roach crusher, which would allow gamers to close the 3DS to smash nasty bugs.
Then there was long-limbed Mario. From what Hayashida explained, it seemed that the Italian plumber would be able to stretch out to crazy lengths. And yes, we all know that would be kind of creepy, but in the context of a Mario power-up, there's a chance it could have worked.
Of course, none of that stuff was actually real. Speaking to Joystiq, Hayashida revealed that all of those insane features were part of one big joke. The director explained that when he speaks to large American audiences, he likes presenting in an over-the-top, comical style. He also stated that the sort of stuff he was saying at GDC and his energetic delivery probably wouldn't get a response from a Japanese audience.
So there you have it, folks. All of those crazy Mario mechanics that were never used were never even real to begin with. I guess it makes sense. I mean, come on, a long-limbed Mario? That is pretty out there.