Ebay (NASDAQ:EBAY) and retailer Kate Spade are doing something this summer that would have been unthinkable just a few years ago: creating a pop-up store in New York that will feature a gigantic touchscreen store window. Let's be clear—what would have been unthinkable would be a relatively small (82-store) apparel chain taking on something this technically aggressive, even with a partner as big as eBay to help foot the bill. Leaving aside all the obvious unanswered questions—from "how do you physically protect a giant touchscreen?" to "how much of an exhibitionist does a customer have to be to browse a web catalog that's taller than she is, right out in public?"—it's a testament to how inexpensive and physically tough this kind of technology has become that it's viewed as practical. Of course, that all assumes that the chain and eBay will actually get it to work as advertised. The project was revealed by eBay CEO John Donahoe, speaking at a conference on April 30. Donahoe didn't give many details about the pop-up store, but he described the concept. "Here in New York, later on this summer, one of the retailers we're working with is going to do pop-up stores with a storefront in which the store window is a touchscreen, so both during the day and at night you can shop and you can engage with their inventory," he said. TechCrunch later learnedthat the retailer was Kate Spade on Saturday. That fits in with Donahoe's notion of shopping that's tied in with a whole collection of screens, ranging from smartphones to tablets and PCs to TVs and in-store displays. The idea of a giant touchscreen isn't new, but the definition of "giant" has changed just in the past several years, from a 42-inch touchscreen embedded in a seven-foot-tall kioskat JCPenney (NYSE:JCP) in 2011 to entire shop windows today. Of course, it's easy to announce a concept (just ask any player in mobile payments). The devil is in the details, or more accurately, in those as-yet-unanswered questions. How willeBay (we have to assume this will be primarily eBay's role) protect the publicly accessible touchscreen front window from abuse? That doesn't just mean the risk of some New Yorker tossing a brick through a very expensive touchscreen—the workaround for that is to use an ordinary window, a little spray-on frosting and a projector, along with technology that senses where a customer's hand is remotely. That way the worst a brick can do is break a window. That approach would also allow an ordinary store window to become a touchscreen without being physically replaced. But that window will still take a lot more of a beating than a standard store window—especially is anything goes wrong and customers start poking at the window with makeshift styluses. (It seems pretty unlikely that eBay is going to replace that pop-up store's window with Gorilla Glass.) How many customers will be able to interact with the window at once? These are fashion customers—they're not going to want to wait to take their turns (after all, inside a store they can all check out clothing at once). And if the software isn't set up to handle multiple customers at once, how much ill will is that going to generate? And what exactly does it mean for customers to "shop and engage with inventory"? Can they go so far as to make E-commerce purchases through the giant touchscreen? If so, it's a very public place to be keying in a payment-card number on a virtual (and presumably not giant) PINpad. If not, what are after-hours shoppers going to do (besides get frustrated)? None of this is to say eBay can't pull this off. But the simpler the concept, the more effort will be required to make it satisfying to shoppers. This one is wonderfully simple—and eBay only has a month or two to make the magic happen.