A chiropractor once recomended a custom pair of shoes to me that cost upwards or 1-2k, -seriously. He took a mold of your foot, video of how you walk, and a special mechine that determined how you distribute your weight on your foot, and stride. That information would be sent to a lab in California, and a month later you would get a pair shoes in the mail. For Those pairs of shoes it would make sense to have a way to change the style, or parts, but I don't see how this would work for the disposible shoes under 500. I believe Nike and a couple other companies have inserts in the heel of the shoe that can be replaced, adding to the life span of the shoe itself. Not a bad idea though, I'm sure it would work for some line of shoes.

For people who care about looking "cool," it would make sense. But your interchangeable parts wouldn't have to be necessary to the functionality of the shoes.

Instead, why not make it possible to attach decals, lighted gadgets and noisemakers instead?

There are still "cobblers" out there who can build up a heel, change the tounge of a shoe, or the color, etc, etc.. why not give a skilled craftsman the work? It's done all the time in theater world! : )