March 10th is the Mario day ( you know... Mar10...), Nintendo already referenced this date in correlation to Mario and it's a Friday, given NX is set to launch in March I'm gona guess that a new Mario game will be available on March 10th .

That is when the android version of the Mario Runner game will come out

https://www.youtube.com/watch?v=uoj1d8x2H6c

It won't be anything really big. Miyamoto said the new Mario game would be shown at E3 if things go well. So it won't be the next installment in the main series.

I don't think so

Nintendo kind of made this up on the spot and is trying to bring awareness, though probably not for games

If it's for the NX, then it would make more sense to be a launch title

Hopefully they will close the 3D World/Land chapter and gives us a fully ambitious 3D platformer without flag, timer, and staticisometric camera.

So, now we know for shure that the Switch will come out in March, moreover Nintendo expects it to sell 2M units in March alone meaning that it can't release in the last weeks of the month and, guess what, a new Mario was shown, is my prediction more beliavable now ?

No they expect to ship 2 million in March, and that's not an especially impressive number, even if it launches near the end of the month. But I don't expect the new Mario game to come out March 10th.