Splatoon would be an interesting release as all the buzz around it and since there are still a lot of people who don't want to buy a Wii U but could be tempted to grab the NX if it looks very promising as a new piece of hardware.
Probably depends of release of the NX 2017 I could defiantly see Splatoon 2 as a launch title but is 2016 may be a little soon for a sequel and would likely see it 6-12 months after.
Couldn't they be both release titles though?