Here's something of interest. According to Siliconera, Nintendo plans to release New Super Mario Bros. 2 as both a physical retail release and as a digital download through the eShop or other digital retailers. People will be able to buy the game either way. Apparently, Nintendo plans to do the same for other first-party titles as well.
Another point of interest: Individual digital retailers will be allowed to set their own prices for the digital version, so buying it through the eShop directly could differ from GameStop's price, and both could vary from Amazon's price.