This is an idea I've toyed with for a while, I called it 'prototype electronics' where the 'store' part had inventory that was known to work together so that projects could be designed, built, and sourced out of the store parts. (this was true early in the RS era as well of course)

There are some annoying liability (ie expensive) issues with letting minors operate soldering irons on the premises or while using solder that has lead in it. But mostly people just don't go out. So when you look at the probability of having enough "customers" you find you need a really large population base while maintaining a very small foot print. New York comes to mind or London. Hard to scale it to more spread out places.