Soundwave on 04 September 2014
I think this has been sitting in Nintendo's R&D for a while, probably for over a year.
I think they also have Fusion (portable) prototypes ready and playable in their R&D and that will launch in 2016.
3DSi ... errr "New 3DS" is just a stop-gap for a couple of years, Nintendo launched the 3DS one year after the DSi XL, and the Game Boy Advance came under two years from the Game Boy Color launch too.
2008 - DSi (Japan)
2009 - DSi (North America)
2010 - DSi XL
2011 - 3DS
2012 - 3DS XL
2013 - 2DS
2014 - New 3DS (Japan)
2015 - New 3DS (North America)
2016 - Nintendo Fusion
Seems about right, Nintendo basically launches a new model handheld almost every year now for like seven years running.
