My guess for the full NX Reveal?
Well.. if they want to launch in March...
Probably January 5th, 2017.
The reason for this?
1. This Christmas season the big money makers will be The NES Classic, Nintendo 3DS software, and a smaller revision of the Nintendo Wii U with a new smaller price to be revealed, alongside Nintendo Selects Splatoon and Super Mario Maker. Oh, and more Amiibo. I wouldn't put it past Nintendo to pack the smaller Wii U with an exclusive Demo Disc for The Legend of Zelda: Breath of the Wild.
2. If the NX launches with a handheld component.. that would hurt the sales of the Nintendo 3DS. If they show off the NX before or after a revision of the Wii U.. they'll hurt it's sales too.
3. I expect them to cram the shelves with budget titles for the Wii U and physical versions of many popular smaller third party titles. I also expect "game of the year" style editions of some games.. kind of like Animal Crossing: New Leaf: Welcome Amiibo or "Splatoon: Competitor Edition." Maybe even a version of Mario Kart 8 or Super Smash Bros for 3DS/Wii U that comes with all of the DLC already. On that note.. I kind of suspect an Amiibo update for Mario Kart 7 was being worked on at some point.
So, January 5th, 2017 reveal alongside an April 16th, 2017 launch date with a mall tour from the end of January to the end of May. Ad campaign really picks up in February with another Direct in March that outlines more about the launch titles for the NX.