My prediction is that when its all said and done, MK8DX will be the bestselling Switch game till the end of the systems life.
The only franchise that has a chance to beat it is pokemon. However, subsequent yearly releases cut off the legs of the preceding title way too early for that to be likely.
Bet with Intrinsic:
The Switch will outsell 3DS (based on VGchartz numbers), according to me, while Intrinsic thinks the opposite will hold true. One month avatar control for the loser's avatar.