I don't think Nintendo's next console will exist in it's own vacuum, rather I think NX will have 2 pieces of hardware, NX itself will technically be the OS, the hardware runs the OS and any games Nintendo makes for it will work on either device.
In this ecosystem a new Zelda made for NX wouldn't be exclusive to the console hardware, but it would technically be exclusive to NX.
The console can scale performance of the games up and the handheld scales down some visual features to make them less demanding, but at it's core the game will play the same and all gameplay features will be intact.
I think the Wii U and NX will both get the most current Legend of Zelda game, so I that wouldn't be exclusive to NX, but there will eventually be another LOZ exclusive to the NX ecosystem, not exclusive to one piece of technology anymore.
In fact I think where 3DS would get a few Zelda releases and Wii U has had to wait the 3DS/handheld Zelda games will come to the whole NX ecosystem and that way Nintendo can release more Zelda games, across the whole install base each generation. Nintendo will be able to sell more releases and move more software that way.
