While flashcards ran rampant in the DS era, the 3DS generation has been protected far more vigorously by Nintendo through firmware updates. There have been numerous exploits and hacks, but users of them have often been driven offline by system updates, reducing their practicality for all but the most committed.
The New Nintendo 3DS has been largely clear so far, with a recent browser exploit - which allowed Game Boy Color ROMS to be loaded and made Pokémon Shuffle free, among other things - only working on original 3DS models prior to Nintendo blocking it off. A homebrew exploit did successfully work on the New 3DS, but was promptly shut-out in another update.
The latest move in this area is that one of the two primary 3DS flashcard providers has released an update that supports the New systems - this flashcard is primarily used, naturally, for loading and accessing ROMS. The beta release has such limitations, however, that it seems Nintendo's efforts at system security have successfully minimised what flashcard companies can offer.
The exploit is limited to firmware version 9.2, while the current iteration on our systems is actually beyond 9.5. In addition another requirement is a physical retail copy of The Legend of Zelda: Ocarina of Time 3D, yet a number of forum users are reporting problems using legitimate copies; others are highlighting how expensive this title now is in terms of physical copies.
While it's a flashcard breakthrough on the New 3DS that Nintendo will undoubtedly monitor, the restrictions and problems users are facing show that security updates have worked so far.
As per our policy we've refrained from linking or naming forums or the relevant flashcard brand. Discussion on the topic is welcome, though please observe the our Community Rules when doing so.
Thanks to RupeeClock for the heads up.