Do it now, before someone takes your name!
So it’s looking a lot like players will finally be able to create proper accounts with the Nintendo Switch, and not have to memorize a long string of numbers whenever they want to add others to their friends list. While the console itself isn’t going to be out for another couple of weeks (a little less than that, actually), you might be able to settle on your username now.
By logging into your Nintendo Account, you’ll see that Nintendo has added a new User ID setting on your profile page. If you’re just logging in now, you won’t have an ID set. You can then choose to edit that field and set a User ID for yourself. Do note that this is different from your Nintendo Network ID, which is used to manage your accounts across the 3DS and the Wii U. The Nintendo User ID is the new one that will likely be tied to your Switch.
The Nintendo Switch is set to be released on March 3.