I don't think there has been any official word on this, but users have reported that some games are region free. I think this is the same system that we had for the Xbox 360. Nintendo do not force games to be region free, but if the developers wish to do it they can. Users have tested the DLC for Breath of the Wild and it is region free, so it seems that Nintendo do not care whether it is or not.
It is always best to just buy the games and DLC from the region you live in though. It can get complicated when you have games from other region and even if it works for you, the DLC might be tied to a game of this region due to some limitations of the law in whatever region you have the game for.