This time around, Nintendo is arguing that by using prod.keys, Yuzu is a copyright protection circumvention product in violation of 17 USC §1201 (a)(2).

No person shall manufacture, import, offer to the public, provide, or otherwise traffic in any technology, product, service, device, component, or part thereof, that—

(A) is primarily designed or produced for the purpose of circumventing a technological measure that effectively controls access to a work protected under this title;

(B) has only limited commercially significant purpose or use other than to circumvent a technological measure that effectively controls access to a work protected under this title; or

(C) is marketed by that person or another acting in concert with that person with that person’s knowledge for use in circumventing a technological measure that effectively controls access to a work protected under this title.

The reverse engineering protection under the DMCA only applies to 17 USC §1201 (a)(1)(A), so there's a very real and very scary possibility of Nintendo winning this one and setting a precedent if they can convince a judge that Yuzu's is primarily for DRM circumvention.