If Nintendo waits until 2018 they are finished in the hardware business.
3DS shipments are targetted at 12 million this year, but they will miss that, probably finishing around 10.5 million. This will be the lowest number of handhelds that Nintendo has sold since 1996 or 1997 (!).
Wii U is just never going to be a huge seller so Nintendo can't rely on that.
The following year 3DS shipments will decline even more to sub-10 million.
There's no way Nintendo can afford to continue that way, they will need a new handheld by 2016. They are badly losing mindshare to tablets/phones every day there are kids being introduced to tablets/phones first and feel that they don't need/want a Nintendo handheld.
The home variant of Fusion won't be anything special IMO. It won't be like some PS4 competitior ... it will be the handheld chip, moderately more powerful than the Wii U (like the GCN - Wii jump). I can see it running games in 1080P vs. 720P perhaps with some more modern shader/lighting effects and more RAM. That would be an OK upgrade. If they use the same chip as the handheld just with more CPU/GPU cores and RAM it'll be cheap too.
That'll be Nintendo's angle ... a super cheap, super-small console (sub $199 to start with, $149.99 quickly enough) that plays all the same games as the handheld.
