Nintendo has been hinting at this for a while. It was going to enter the mobile market eventually so the question wasn't if but when.
I doubt these games are anything like what most are expecting. I've already seen one site say "fingers crossed for a full Pokemon game coming to iOS soon." I think people are going to be really disappointed if they think Nintendo is making anything remotely close to the scale of Pokemon X/Y for smartphones. Nintendo may redefine the value and quality of mobile games (like it did with DLC), but if people want the full experience of Mario, Zelda, Pokemon etc., they will still need to buy dedicated Nintendo hardware. Like motion control games on Wii, these mobile games and apps are likely meant as "gateway drugs" to the games Nintendo really wants to sell people. Any converts are people who weren't buying Nintendo products before anyway.
I'm already rolling my eyes at anyone who thinks this is the beginning of the end for Nintendo's hardware business. That isn't going anywhere. Nintendo has likely agonized for years on how to leverage the mobile market in a way that benefits its own hardware. I don't think Nintendo is worried about cannibalization because while mobile games and console games are both categorized under the general "games" umbrella, there's very little overlap as far as experiences go. Nintendo wants people to transition to its dedicated hardware. Not sure how many people actually will, but it's worth exploring.
As for NX, what if it's actually "N Cross," a console-handheld hybrid?
HashtagBlackNMild
(I'm still betting on Nintendo going one more generation of keeping console and handheld separate.)