Pretty interesting idea. I'm actually surprised this hadn't been done sooner. Steadicam is a very reputable brand (they make the high-end stabilizers used in Hollywood, etc.), so the quality should definitely be there.
While the overwhelming majority of GoPro videos are not shot with additional stabilization, as mentioned in the post above, the support used behind GoPro's official videos is pretty intense. I recall seeing a BTS photo of them operating a Glidecam HD4000 for stabilization at one point, as well as a gyro for the Ryan Sheckler piece a few months ago. I don't think it's overly imperative to use such tools for a small camera, but it definitely could be that extra piece of equipment to differentiate your work from other GoPro videos. In my opinion, it would depend on what exactly you're using the footage for. If you are simply tossing a camera back and forth skiing with friends, I personally wouldn't get the Steadicam. However, if the GoPro is your b-camera, or is being used for a few super wide gliding shots for effect, I would consider it.
Just a few thoughts,