WarioWare: Twisted! was one of my favorite GBA games, and it's built in gyroscope was pure genious. The 3DS is going to have this tilt sensor built in, then throw in the touch screen, cameras, and you have the potential for the best WarioWare game ever made. I don't wonder if this will be a 3DS game, I know it will.
I take it that you have never played it? Its wasn't in 2D and had many 3D elements.
Besides a game doesn't need to have 3D to be on the 3DS. Look at the NDS, many people want a 2D Metroid where the touchscreen would probably be ignored in the gameplay.
You can even have 2D games take advantage of the 3D features of the 3DS, anyone who has experiences Wario Land VB will know this.
^ this plus having maybe a slightly 3d element to it think like Bleach DS with front and rear rows but instead of jumping between them you can walk up n down between them and fight!