The 3DS and Wii U shops' days are numbers. In a new support page, Nintendo has revealed that it's shutting down the eShops for the Wii U system and the 3DS family of consoles in late March 2023. That means after that date, you won't be able to purchase any content from the shops anymore, download demos and redeem download codes. The shutdown process will start much earlier than March next year, though: You won't be able to use a credit card to add funds to your eShop account starting on May 23rd, 2022.
Further, while retailers will sell Nintendo eShop Card cards until supplies last, you can't use them to add funds to your account anymore starting on August 29th, 2022. You can add as much funds as you want until those dates, however, and you can redeem download codes until late March 2023. After the eShops officially shut down, you can only use them to redownload any content you already own and to install software updates.
Nintendo wrote in the FAQ section of the page that the the move "is part of the natural lifecycle for any product line as it becomes less used by consumers over time." Both systems are getting up there in years, and Nintendo stopped manufacturing the 3DS back in 2020. Meanwhile, the Switch has become Nintendo's best-selling home console last year after selling a total of 103.54 million units since it launched in 2017.
As Kotaku notes, Nintendo is also removing the only way to buy some classic games for older platforms by shutting down the shops. Apparently, the gaming giant deleted a section in its FAQ talking about how the Nintendo Switch Online "is an effective way to make classic content easily available to a broad range of players." It added: "We currently have no plans to offer classic content in other ways." Nintendo Switch Online is a subscription service, though, and you can only access its library of classic games as long as your membership is active.