I think they'll be done by 2017, way too late.
3DS is going to be shipping sub-10 million units by next year. And Wii U is never going to be a big seller.
Mobile/smartphones are a bigger threat than Sony/MS ... I think people are still in denial about this, but kids are jumping off Nintendo's bandwagon every day.
Really Nintendo needs a new handheld for 2015, even 2016 is fairly late. 2017/18 would incur a lot of damage to Nintendo's business and mindshare IMO. Tablets and phones are taking the 3DS to school and beating up on it, Nintendo needs to send reinforcements sooner.
The 3DS is starting to decline noticably in 2014 ... it won't make it to 2017.







