I think it could be done while keeping all 3D model data on the client. I'm picturing something akin to a computer game, where people install the game/tool on their PC. If you've ever created a detailed RPG character, that's what I imagine it to be. Something where you can sit and browse real clothing/accessories/makeup, and fit it onto a detailed, exactly proportionate 3D model of yourself, then add the entire ensemble to your shopping cart would be a very killer app. Oh, and then you could have mods for 'if I lost 20 pounds' '3 months pregnant' and sell people clothes they don't need yet and may never fit.

This is probably something Facebook or Google should do. They already have the users, if they had something functional like this they could get a significant cut of the global retail industry overnight.

Once you had that working, you could go about providing the same model for homes, interior and exterior. And buy Fedex.