The best idea for an online shop is selling games and streaming videos or something. There are so many people who loved to game and dont want to spent there gold into it they have bitcoins where they dont do anything with. So they can buy games at your site and videos that would be very great trust me.
If you need open online shop for bitcoin means just try to put big investment and open one Ecommerce site which can accepts bitcoin as payment and payment gateway. If you want do online shopping means try to check the sites by Google it.