Last year, Nintendo unveiled a new tier of its online service, the Nintendo Switch Online Expansion Pack, where upgraded subscribers would gain access to a select number of classic Nintendo 64 and Sega Genesis games. While the news was met with excitement at first, the plan's price muted fans' expectations. It was further hampered when the initial release had left fans frustrated with the Expansion Pack's N64 emulation problems. Some issues fans had included input lag, low frame rates, texture problems, and missing features just to name a few.
One of these missing features from the N64 Nintendo Switch Online version was support for the Controller Pak. For the uninitiated, the N64's Controller Pak could be considered the console's memory card. These were placed on the back of the game's controller, which would allow players to save game data when some games weren't saving directly to the cartridge. This was more common in older games released on the N64, with third-party games, such as WinBack Covert Operations, having a reliance on it. Other games like Mario Kart 64 uses the Controller Pak to save optional data that is too big for the cartridge. One hacker was able to restore this missing feature into the Nintendo Switch Online N64 emulator.
According to LuigiBlood on Twitter, they had datamined through the files of the Nintendo Switch Online's application, discovering this function had always been a part of the Switch's N64 emulator. The coding, however, has only disabled this feature, where they then shared instructions on how to restore its functionality, with another hacker being able to provide evidence that this solution would allow players to use the Controller Pak again.
This evidence is a video of Mario Kart 64, where thanks to the restored functions of the Controller Pak, it allowed players to save time trial ghost data to the game. They did note that as soon as the game was turned off, the saved file would disappear once it booted up again, meaning that the hack is seemingly not possible on the retail version of Nintendo Switch Online.
LuigiBlood commented that the content saved in the Controller Pak this way is kept in a save state, but not when it restarts, so it's possible to be used with some additional tweaking. He further notes that if there are future plans to implement this feature into Nintendo Switch Online, then there wouldn't be a lot left needed to be done in order to get it live for fans. With reports that the Nintendo Switch Online service is improving its emulation, it's possible that this feature will be officially restored in the near future too.