If the dual gamepad thing is true, it would suggest to me that they plan on keeping the wii u alive a quite a bit longer. E3 will be interesting because we'll be able to get an idea for what Nintendo has planned medium term meaning the next few years especially by what is not announced. If the Wii U announcements are somewhat underwhelming, then I think there is a strong possibility they cut the cord 2016 and they release their new console late 2016, if medium, then 2017. If they do the dual gamepad thing 2017 soonest perhaps even 2018.
Right now, I'm expecting new handheld late 2016, and then their new console 2017, still possibly 2016.