It's just a tech demo. I have a hard time seeing MS bothering to market and promote a commercial release of Geometry Wars Natal to sell the public on Natal.
While I'm sure it could be an entertaining alternative control scheme, for something like Geometry Wars, one only has to ask "does it make the game easier to play" as in will using motion tracking controls allow me to handily top my old high scores. If the answer is no, then it's just "an entertaining alternative control scheme" that doesn't offer any benefits in improving player/game interface.
I'll wait until we start seeing games designed specifically for Natal from the ground up before I start to feel any sense of anticipation.
I'm still buying it, but I do hope to be seeing something new and original, even if the early efforts happen to be along the lines of those PS Eye games SCE used to make one upon a time (whatever happened to the game support for that?!).