That's the killer. It was so obvious. Having Splatoon release so soon after really killed ARMS. Everyone knew this. It was so captain obvious. I believe Nintendo caused this by the poor release timing on ARMS. We all realised this long before the release of both games.
I seriously hope not. Most of the annual games end up being barely updated versions of the previous year's games. Nintendo are best sticking to one game a console to give more time for the developers to amke a good game, not just a quick cash cow.