If 2015 is not kind to the Wii U, I expect we'll be hearing about a new console underworks in 2016 E3, and release it in 2017 sometime (middle or end of the year). Of course, the new console is already underworks, but Nintendo will announce it sooner (imo) if things look bleak for them.
What do I think Nintendo should do? Hold onto the Wii U for a long time and allow hype for their next gen console to heighten by sheer expectations, and also to wait out the life cycle of the PS4/Xbone, and give them the proper amount of time to create something that can surpass the PS4/Xbone by enough of a margin to make it feel like gen 9 while also remaining cost effective. They need to ensure that they understand the ballpark power of Sony/Microsofts next gen consoles, and then replicate it closely enough before they decide on the power too quickly. Waiting it out for a longer period of time increases the chances of getting an idea of that.
Nintendo should never again aim for ports of previous gen titles. What they want is new games and to share 3rd parties with Microsoft/Sony. Their consoles should be around the same ballpark in power and capability of their competitors so that they can share multi-platform titles more easily.
