The Nintendo Wii U and 3DS eShop are receiving two separate discontinuations over the course of the next eight months. Starting August 29 of this year, users will no longer be able to add funds to their accounts on either platform. However, it won't be until March 27 of next year that purchases will not longer be possible.
If you're a Wii U or 3DS owner with a bucket list of games they plan to complete on either platform, now is your only chance to do so. Once these dates are reached, Nintendo will officially begin shutting things down. Take the time to browse through each game's eShop and make your final purchases (or at least add funds to your account) before August ends.
This doesn't mean you won't be able to play purchased games, though. Nintendo made it clear that, even after March 27 of next year, you can still download games and DLC you already own. Software updates and online play will also still be available for both consoles for "the forseeable future," but keep in mind that this may imply that these may be taken away at some point.
For some unknown reason, sales for Fire Emblem: Fates will no longer be possible starting February 28 of next year. It's strange than Nintendo specifically singled out this game in particular, as we have no good justification for it as of yet.
It's always unfortunate when legacy consoles get these kind of updates. In a lot of ways, it makes a potent argument for why the digital age of gaming isn't what it's cracked up to be. It's great when the console is in its golden age, but once it's old and abandoned, your ability to access those games relies on the company itself. If Nintendo suddenly decides to prevent users from downloading games from their digital library, we're all gonna wish we stuck with discs and cartridges.