3DS successor will launch in spring/summer 2016, book it (5 years after the 3DS).
3DS is simply not strong enough of a platform to warrant a 5+ year lifecycle, it's already fading fast, even in Japan the introduction of a New 3DS model can't boost it above its previous years sales even for more than a couple of weeks.
This thing is sinking and fast. Nintendo's yearly handheld shipments are reaching lows that haven't been seen since before the launch of the GBC and Pokemon in the late 1990s.
That's ok though, there's nothing wrong with a 5 year life cycle. If Nintendo could do this gen over, I gauruntee you they would not give the Wii a 6 year cycle ... that was simply too long and they lost too much brand momentum because of it. DS lifecycle was also a year too long.
If they don't provide a real next-gen hanadheld update they are going to completely lose even the kids market, because the 3DS is laughably outdated compared to modern iPads/iPhones/Android tablets that have larger, higher resolution displays. Kids are not impressed with the 3DS anymore, it's yesterdays news.
Not coincidentally though by 2016, having Wii U level or even better graphics should be fairly easy to accomplish with a mobile chip. The new iPad Air 2 is honestly probably as powerful as the PS3/360, there's just no games that show it off, but it does have the raw horsepower now. By 2016, that level of chip will be even more affordable and powerful. Perfect for Nintendo. Interestingly too, AMD is claiming they have two big mobile contracts with big vendors won for 2016 that will integrate ARM ... that sounds a lot like a Nintendo handheld contract IMO.
