Nothing truly lasts forever. That's a universal law when it comes to all things in life, especially with the video game products we love to enjoy. New systems eventually get older and the support for them is taken away, leaving online servers and functionality completely abandoned. The digital storefronts for those consoles eventually become dormant, and prevent anyone from buying games through them, forcing players to move on to newer platforms. This is something, as a Nintendo 3DS owner, I'm very familiar with. And I could see an eventual repeat of what happened with the 3DS down the line for the future of Nintendo Switch 2.
One of the latest features coming to Switch 2 games is the introduction of game-key cards. Unlike the original Nintendo Switch cartridges, these game key-cards only contain a digital code to download a game from the eShop. They do not contain the full game at all. Although this might be convenient for Nintendo and its players now, this could be the seeds of a future problem that is reminiscent of what happened with the Nintendo 3DS. It begs the question, what happens with game-key cards when the Nintendo Switch 2 loses its online support in the future? It's something that makes me worried the more I think about it.

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Downloading Games Through Game-Key Cards
When the eShop goes down?
Game-key cards for Nintendo Switch 2 only contain a key to download the game you purchase. Putting the cartridge into a console automatically triggers a download from the eShop. And once the game is downloaded, it will play like any other Switch physical game cartridge. But what happens when the eShop is no longer supported, or if the digital store is taken offline for some reason? If the game is already downloaded onto the Switch 2, then it shouldn't be a problem. But what if it's not, such as when someone picks up a used game from a store or obtains one from a friend? You can't download the game at that point, which makes the game key card useless. And from what Nintendo has released to the public about upcoming Switch 2 games, most of the titles announced for the console will be like this.
When the Nintendo 3DS digital store went offline, gamers were not able to purchase new games for the handheld, but they could still download the games they already owned. The only things locked off were demos and new purchases, which included downloadable content. But it's uncertain if the same thing would apply to Switch 2 games when the eShop is inaccessible for any reason. The scary part about this is that that even though you have the cartridge with the key, you still wouldn't be able to download and play your game without a connection to the digital store.
The Used Games Market
What happens if I buy used?

Source: Nintendo
The biggest concern about this will inevitably be the used-game market, and what solutions are reasonable when games are resold to other people. Are the keys within the game-key cards tied to a specific Nintendo account when used? Or is the key within the card reusable when shared between different Nintendo Switch 2 consoles? These questions have no real answer yet, even though Nintendo has lightly addressed them since the reveal of the Nintendo Switch 2 or the use of game-key cards. It's a real concern many people have, since games are often shared or resold, even with games on new consoles.
Nintendo 3DS titles never had this kind of issue, since the full game was always available on the cartridges themselves. The only problem was expansions and other downloadable content for games that you couldn't buy after the digital storefront was shut down. But having the base game is better than having nothing at all, even if I miss out on some good DLC. Unfortunately, I'm unsure if I can say the same about the Nintendo Switch 2. I find myself thinking about what it might be like years from now, and how these games will be preserved when they're mostly available through digital means. I might own a copy of Metroid Prime 4: Beyond for my Switch 2, but will I always have access to it, despite having the physical unit? It's a very scary thought to have.
The far future for Switch 2 games
While many of these concerns won't sprout into full problems for years to come, I feel they are still valid concerns for anyone buying the next Nintendo console. Much of this has never been a real issue for gaming consoles in years past, mostly because a physical copy of a game meant that the actual game was actually within the physical unit. However, as technology changes and game companies move on to new platforms, new consumer problems will eventually emerge. The Nintendo Switch 2 is only just getting started with its lifespan, but it would be very wise of Nintendo to find ways to address these things early on before it's too late. Remember, nothing ever truly lasts forever.

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