I had discussed a Kinect idea with some fellow employees when I worked at VS and they scoffed at the idea.
I think the issue is that breasts are more complex than just external shape with internal density and natural placement being just the tip of the iceberg. All the factors involved rule out a cheap modeling method such as Kinect or webcams and in the end, make visiting a store, to be measured properly and try for fit, the more economic choice.
I don't think you can get by the trust issue, but a redboxish booth to be placed at stores might work. I know I would really like to order jeans / pants customized to fit. Not sure if I wound stand there in a booth in my skivvies to get scanned. Imagine being topless for a girl would require a fair bit of trust.
I think the issue is that breasts are more complex than just external shape with internal density and natural placement being just the tip of the iceberg. All the factors involved rule out a cheap modeling method such as Kinect or webcams and in the end, make visiting a store, to be measured properly and try for fit, the more economic choice.