I agree that vaporware has been successfully marketed before, however, that is not my idea of creating value, so I agree that it depends on how one defines value, and I would not want that - marketing non-existent products - to become the meaning of value within the context of a tech startup, that is best left to a marketing/publicity outfit if you ask me. I also think it is wrong to conduct market studies under the guise of a real product offer.

What happens when it turns out that the bullet points with features cannot be implemented, or are simply not the best solution for the users?

I find pg's thoughts on the subject of how problems may end up being redefined as they are being worked on to be very wise advice.