https://accounts.nintendo.com/Nintendo already started putting an end to their awful and dated "your digital games die with your console" policy with Nintendo Network IDs, but now they're introducing accounts where you can tie everything together with all your separate Nintendo consoles (including the upcoming NX), websites, and mobile games (like Miitomo). It'll also be used for Club Nintendo's successor, "My Nintendo." Current functionality is limited to...well, pretty much nothing, but you can at least create an account, either from scratch or with your NNID, Google+, Facebook, or Twitter.
Welcome to the 21st century, Nintendo! Nice of you to join us.