This seems interesting but very easy to take advantage of by either party. If I were the buyer, what if I transferred the coins somewhere and then claimed that the seller transferred the coins out before I had a chance to do it myself? And vice versa, if I were the seller, I could do exactly that but prove to eBay that the USB stick with 'free' wallet arrived correctly.
Either way, one of the parties will get cheated, and as soon as this becomes a regular occurrence then I imagine eBay will take steps to forbid trading in digital wallets.
The best developers I know have the experience to know when each is required. Getting the right balance between speed and quality is one of the things I find hugely valuable in a developer, usually more so than their maximum coding speed or maximum output quality.