They are still running afowl of the anti circumvention rules in the dmca. Just saying you have to provide your own keys isn't enough.
A switch emulator that wants to be safe from nintendo has to have no capability of circumventing the copyright protection mechanisms nintendo employs.
Look at vlc for inspiration. It can play blurays, it can't circumvent the copyright protection of blurays. But if you provide the keys and the library that decodes the content then it can play them just fine. This keeps vlc safe.