Splatoon as an IP would really work well as a turn based strategy game like X-com. Different gear is there, a multitude of weapons etc.
But that won’t happen (or at least I hope it won’t happen) because Mario + Rabbids happened (which is a good game).
Mario and Rabbids is a very good game. But I wouldn't count a turn based Strategy spin off out just because of that. Nintendo tried it before with Codename Steam and if the team behind Kingdom Battle really wanted to build in roads in Japan, a Splatoon crossover (maybe not with the Rabbids but Rayman proper) would probably do quite well in Japan with a similar or equal level of care and Polish Mario and Rabbids got.
But yeah, I don't see the eventual Splatoon spinoff until 2019, this year is all about hyping the Octo DLC and various Splatfests.