Here are the beta elements of Mario Kart EXTRA!
On Nintendo Power, it says that Bolt Highway (bolt_course) and DS DK Pass (classic_dk_course) are gonna appear, but the idea is removed. There is also files for the beta tracks.
Track Names & Looks
Retro Hills was originally going to be named Classic World and was going to look like World 1 from Super Mario World, but was changed.
The items are going to be a Burning Shell (1x/3x), a Frozen Shell (1x/3x), a Goomba Herd, a Thunder Cloud, and a Rain Cloud, but were all removed.