If they're released separately (big if), I'm almost certain the console is coming first. Wii U has nothing left besides Zelda and that is cross-gen. 3DS is winding down but still has a handful games of left such as the Dragon Quests and Pokemon, and a few more could be made cheaply as a stopgap. Plus the 3DS has no real competition in its dedicated handheld space.
Lets say i follow you, the nx is a console. After a few years ps5 and new xbox is released. What will happen with the nx support? Almost no 3rd party support. It's getting way too expensive to make games for one console or to downgrade the games. This happened for wii and wiiu. 3ds is still not bad, but the games aren't also that expensive.