in a way i agree with you, but you phrased it wrong. i don't think underground/rebel/punk has to go anywhere, people will always express themselves in whatever way they want.
the issue here is not for the "image" to go away, but for the image to expand and include older folks. A company like Never Summer who caters to more of an adult audience, is a good example.
Yup, snowboarding needs to be more inclusive. We need to keep attracting young kids who snowboard in their back yards as well as the winter sports enthusiasts looking for a new way to challenge themselves.