Tradition would say that, but a weekly sub 30k is far more powerfull then any tradition. Annoucing and Launching both handheld and console at 2016 is perfectly possible with the will do so. And that will will grow stronger every day with those sales.
I wouldn't even be surprised to see Nintendo break their promise to show anything about the NX at this E3. They need any positive news and just showing off the NX concept could instill that in developers and the overal market.
The WiiU hasn't even hit its first price cut yet and launching both a Handheld and a console in the same year is something Nintendo would want to avoid in order to reduce sales cannibalism. (I believe the only time they released both a console and a Handheld in the same year was 2001 GBA/GC).
The WiiU still has life in it yet, I'm putting my money on NX coming out 2017.