Sure, you cannot market to customers based on their wishlist articles as easily, but you will increase the likelihood tenfolds that your customers will actually share their lists with others. If a list is specific to one shop, the users don't want to share it, but if they have one list that covers all shops, they will do so. So, by providing your own wishlist service in order to track your users, you don't actually get so much to track.. So, you can actually skip that point and gain much more from a more shareable list. It will make you more marketing and sales. And you can still target your users through abadoned shopping carts.