Nomura's statement earlier this year implied that Dark Road was the only mobile KH in development. Chances are the other 2 new KH games coming before KH4 are either Switch exclusives, or multiplat (Xbox/Switch/PS).
It just wouldnt make sense to make it Switch exclusive. They HAVE to make the game compatible with a regular controller on the Switch since its a hybrid, so why not put it on the other consoles and make way more money? Also they have released The Complete Story on both PS4 and XB1, so I dont think they would make another console version not available to that fanbase.
The only reason I could see them do it would be if they made a deal with Nintendo. A very expensive deal for Nintendo.