I think we'll see the reveal sometime in the next 5 weeks. Nintendo have done quite a few things in the last couple of months (intentional or otherwise) that have been a long time coming in terms of planning.
We've had the 3DS Direct, which confirmed what'll be coming for the portable through 2017, which was, I think, the last time that system gets a starring role. Additionally, last year's E3 showing, and then the news at the start of their new financial year that Wii U shipments would be reduced to 800,000 and Zelda would be cross-platform, confirmed that meaningful support for Wii U was at an end.
On top of that, the launch of the new account system and Miitomo demonstrated at least some of the groundwork for Nintendo's evolved online offerings that are designed to encompass mobile and NX. The appearance of Mario at two incredibly high profile events--the Apple keynote and the Rio Olympics--helped to push Nintendo's brand awareness to new heights. Combine that with the unprecedented success of Pokemon Go and the positively received reveal of the NES Mini, and Nintendo have so far done a fairly decent job.
Lingering concerns about their software output (after Tennis U, Amiibo Festival, Star Fox Zero, Federation Force) need to be put to bed at the NX announcement with some big software reveals, but Nintendo have cleared the ground of other Nintendo related news. We know Wii U is done, we know 3DS has support coming into early next year, and we know Nintendo are going big on mobile with Pokemon and Mario.
Now we just need to know about NX. I think that information is coming soon.







