This upcoming 'shared' architecture isn't going to make any difference.
A game targeted at PS4/XBO won't run on the 4DS.
The point is that a dev can make a game that plays on all the home consoles or handheld of optimize it for both and that Nintendo will make games that play on all their platforms.
So if EA wants to make BF5 for example, the more powerful home console will be ok to play it while the handheld won't, but Ubi can make a Rayman optimized for both home and handheld.
It's like those games that require ipad to play but won't play on an iphone for example while others play on all iOS devices. The amount of power needed to play the game will be up to the developer while all devices will share the same architecture and OS but different stats.