Okay, it's now pretty much confirmed that Inazuma Eleven Ares is a Switch game, as...there's not really any other option.
Hino revealed first screens of the game (barely started development with no release date) :
As you can see, it can't really be a 3DS game with that level of graphics. So there was two options left : mobile and Switch. But it's not the former either as Hino showed a few minutes later that there will be a companion app on mobile, implying that the main game won't be one :
So there it is, you have one Level-5 game in development.