You guys have got to be kidding right? Their software sales across the board (mainstream+niche) would grow exponentially, software revenue would double at the absolute minimum.
1) NONE of their games would reduce in sales, thats just silly. 99% of what Nintendo produces is at the top of its class in terms of genre and more often then not, there is not strong compition coming from third parties. There are almost no decent budget games on PS4/X1 like Captain Toad, Pikimin, Wonderful 101, Splatoon etc. Beyond that Nintendo's audience wouldn't suddenly vanish if they went third party. Even as things stand, I doubt most people own a Wii U exclusively, meaning that Nintendo's games are already in competition with third parties and even if you did only have a Wii U, that means you obviously want Nintendo's games above third parties. So third parties are not a massive threat to Nintendo's success.
2) There are no comparisons here to support a lot of the logic people going by. So lets take a look at the most recent Skylanders, a games which audience is obviously skewed towards young kids.
Wii U: 380k
360: 350k
PS3: 300k
PS4: 250k
Xbox One: 170k
Even though the game performs best on Wii U, the sales of the game is doubled from 380k to 800k when you add the PS4/XO's sales on top.
Now lets look at Rayman Legends. A game that although is very child friendly, is made for people of all ages to enjoy (closer to the typical Nintendo title then Skylanders)
PS4: 800k
Wii U: 600k
Xbox One: 300k
Multiplatform is never a bad idea unless it affects the quality of the game or potential funding from sony/microsoft (obviously not relevant to Nintendo)







