Nintendo initially indicated that they will be revealing more details about the Nintendo NX this year and with Nintendo confirming that they will be at E3 this year everybody assume that we will be hearing about the new Nintendo NX console at the E3 2016 but that is not going to happen.
Nintendo has already revealed their plans for E3 2016 and so far, their plans seem to revolve around the Legend of Zelda for Wii U. Not only will they be releasing some additional detail about the game but those at the event will also get to try out the game on Wii U at their booth.
There was no mention of a Nintendo NX announcement and it felt like Nintendo only wanted to focus on The Legend of Zelda for now.
It is believed that Nintendo plans to release the new console next year so that they have ample time to come out with games for the console before it arrives.