I think this will end up happening - Amazon already lets you suck out it's catalogue and push affiliate sales back to it. You could likely build very sophisticated niche virtual retail sites if all the bricks and motar data was there also.

Interestingly in the survey the number of ecommerce APIs was actually a lot lower than we thought it would be. This might be a blip in this "generation" of APIs, or that it's simply hard to do still.