I'm just saying for every argument made that the handheld should launch first there are equal arguments for the opposite
You say out your strong foot forward, I say the strong foot can handle its own, replace the weak foot first.
The 3DS isn't selling DS or even GBA numbers but it's still doing decently and getting big games in 2016. Especially the second half of 2016. And we all know game freak is slow to adopt new platforms so Pokemon Z or X-2 and Y-2 are gonna be 3DS's swan song. Why replace the handheld when major blockbusters like that are being released?
The Wii U has Star Fox, a title that will bomb if it's preview impressions are any indication, SMTxFE, a niche jrpg that will be loved by critics and us, but sell like shit, Minecraft DLC and Pokken will sell well, and Zelda. The unannounced game is more than likely Paper Mario.
But the Wii U schedule is a lot more barren and spread out while the 3DS is more consistent and has some holiday titles.
Kill the weakest link first and launch the NX with the heavy hitters and then continue the momentum of the holidays with a handheld release in Q1 2017.