The biggest downside to touchscreens is the 'gorilla arm' syndrome. You end up having a forearm like a gorilla (or popeye) from the effort to keep your hands raised to use it. It's one thing to have a touchscreen on an intermittently used device like a keypad or tabletop remote. But the whole idea of a "minority report" style touchscreen is just a chiropractors dream.
That and cleaning up the fingerprints on the glass.
Still, it would be cool just from the gadgetry standpoint.