Soundwave on 17 March 2015
I'm guessing this will launch for next year (fall 2016).
Also they don't say if its a console or portable, Iwata just called it a "platform".
This is the direct quote:
As proof that Nintendo maintains strong enthusiasm for the dedicated game system business, let me confirm that Nintendo is currently developing a dedicated game platform with a brand-new concept under the development codename “NX.” It is too early to elaborate on the details of this project, but we hope to share more information with you next year.
