Even if we look at the DS-3DS transition
Last 3DS revision (DSi XL) launch in Japan in November 2009. 3DS launched in Japan in Feburary 2011.
That's roughly a 14 month gap. 14 months from New 3DS to Fusion would be Feburary 2016. So a March-May 2016 launch in Japan would actually be a little longer of a gap.
Ditto for the US, DSi XL launched in March 2010, 3DS launched in April 2011 ... 13 month gap between the two.
GBA SP-DS was about a 1 1/2 year gap.
In fact I'd say the New 3DS' timing hints fairly strongly at a new handheld generation beginning in 2016.
Not only that but AMD reports that they huge "two major vendors" that are big contract wins for them regarding an ARM based AMD mobile part for 2016.
That sounds an awful lot like Nintendo could be one of those contracts, especially when Iwata said he wanted future Nintendo platforms to "absorb" the Wii U architecture in some way (that probably means they have to use AMD). So that all lines up rather nicely.
