Demos already exist.
They're for Metal Gear Solid: Snake Eater 3D, Mario & Sonic at the London 2012 Olympic Games, Resident Evil: Revelations (or is it the other one?)... basically, they're for games that have finished. They're hardly going to put "Paper Mario 4", if that hasn't even been announced for a release date.
Demos already exist.
They're for Metal Gear Solid: Snake Eater 3D, Mario & Sonic at the London 2012 Olympic Games, Resident Evil: Revelations (or is it the other one?)... basically, they're for games that have finished. They're hardly going to put "Paper Mario 4", if that hasn't even been announced for a release date.