Food for thought, Disney would be indirectly earning money off of this through figure sales, game sales, and a longer lasting player base. Not significantly so, but all the new content adds up.
Additionally, if this mode were a homage, reference, or parody, Disney can not mention Nintendo or Splatoon. If we were to assume that Disney did not receive formal permission, the mentioning of Nintendo or Splatoon only gives Nintendo more to work with in an unlikely but possible lawsuit. Simply mentioning any of these two names, let alone announcing your mode as a reference to these, is to blatantly say that you tried to rip off Splatoon without permission. At worst, Nintendo would use that against you and somehow win the case. At best, you just gave Nintendo advertising you could have made money off of, and upon realizing this, Nintendo puts the phone down and a Splatoon advertising deal that was just about to be brought up never sees the day of light.
Or maybe Nintendo still ignores it... But that's not interesting.