3DS firmware 11.8 potentially brings the Switch's method of piracy detection
Looks like this is it. According to a tweet from SciresM, the latest 3DS firmware update 11.8 has ported the Nintendo Switch's piracy detection systems to the console. This strategy enables Nintendo to perfectly distinguish pirated and legit games going online and has been used before to detect and ban pirates on Switch. This is not something that can be avoided with homebrew. According to SciresM, Nintendo hasn't acted on 3DS pirates yet, but can choose to do so any time in the future.
Be careful, guys.
Looks like 11.8.0 backports the Switch's aauth ideas to 3ds -- network comms now send an encrypted(?) copy of app ticket to the server.
— Michael (@SciresM) July 31, 2018
They may not act on it immediately, but like on Switch this lets N perfectly detect pirate accesses vs normal ones, and ban however they like.