Nintendo won't be dropping the Wii U in 2014, or 2015.
The soonest we might possibily see the next Nintendo home console in stores would probably be November 2016. That would be the earliest. It might not be released until fall 2017.
Naturally Nintendo will be watching carefully to see how much Mario Kart 8 and Super Smash Bros Wii U boost hardware sales this year.
There is also, of course, the next main Legend of Zelda game "Zelda U" as most people refer to it. That game could easily be revealed for the first time at this years E3 in June, and be released in fall of 2015.
Nintendo no doubt has some other aces up its sleeve for Wii U, to keep it alive over the next several years.
However it's pretty damn clear, at this point in time, that Wii U will probably not be on the market for 6 years (since fall 2012) before its replacement is on sale.
It also goes without saying, Nintendo is not Sega.
Nintendo has no doubt carefully studied ALL of Sega's mistakes, including the comment at E3 1997 by Bernie Stolar when he said "the Saturn is not our future", 2 years after Saturn's limited initial May '97 U.S. release, and about 2 years before Dreamcast's release in the western world.
Nintendo is not going to suddenly drop Wii U hardware, or support for it.
I would imagine, barring some incredible turnaround, Nintendo will execute a careful, phased withdrawal of Wii U. They'll be mindful not to piss off Wii U owners, and also not to piss off the legions of Nintendo fans, or the public in general, all of whom Nintendo will be counting on to support its next console and next handheld sometime during the second half of this decade.