PS4 unveiled June 2013 - Launched November 2013
XBox One unveiled May 2013 - Launched November 2013
Nintendo 3DS - Announced March 23, 2010, Released (Japan) February 2011.
Wii U is actually the odd one of the group and seeing how it's by far the worst selling of that group, can't see why Nintendo is obligated to follow that formula in any way.
Nobody wants to see hardware, get excited about it, and then be told to wait 1-2 years for it to release. That doesn't fly today it's not 1997 anymore.
Nintendo probably could show the NX right now, but it would cause already weak Wii U and 3DS sales to likely crater for the holiday season so there's no logical reason to show the hardware this early. They'll show it after the holidays are done, my guess is probably around March (fiscal year end), if not just wait outright for E3.
