If you look at the history of Nintendo and their consoles, you see that they tend to release new consoles that lag behind in technology, them release newer consoles only a few  years down the road ( see Gameboy Color, followed by Gameboy Advance, then DS all coming out roughly in the space of five years).

This console gen they discovered that a new console aimed at the right audience ( largely nongamers) and at the right price can become a fad and make them a lot of profit in the short run but be doomed to failure in the long run.  See Wii's position in the marketplace the last two years since it simply didn't have the hardware to compete with Microsoft's Xbox 360 and Sony's Playstation 3.

More than likely we will see a similar situation occurring in the next two years when Sony and Microsoft release their new consoles.  Wii U ( which has already shown that it doesn't have the same level of demand that the Wii and 360 had at their launches) can conceivably do well against Microsoft and Sony's upcoming consoles in its first year as it will be getting by on ports from the 360 and PS3 during the short term whereas Microsoft and Sony's next consoles' lineups may not be all that impressive at launch.  However by the Second Christmas for the follow ups to the Playstation 3 and Xbox 360 all the True flashiest and most anticipated next gen games will be launching for 720 and PS4 and the vast majority of them will be far superior to any Wii U versions in much the same way that 360 and PS3 versions were to their Wii counterparts (the few that were released).  Yet with more consumer friendly pricepoints for their new consoles than their predecessors had in addition to still maintaining the power to make Wii U look as obsolete as 360 and PS3 made the Wii look, market penetration of the 720 and PS4 will be much more rapid than it was for 360 and PS3.

In effect, Christmas 2014 will be in favor of 720 and PS4 versus Wii U just as much as Christmases 2011 and 2012 were for 360 and PS3 versus Wii.

So, do you expect Nintendo to launch the successor to Wii U in 2015?

If you look at the history of Nintendo and their consoles, you see that they tend to release new consoles that lag behind in technology, (..)

This is all I read. Why? The first sentence is already wrong. They launched a system which lagged behind in technology (power-wise at least) only once.

OT (judging from the title): No, not until at least 2017.

Why are these to only two options? The first option is an extreme, the second is getting there. Why not a moderately powerful console with a focus on hardcore gaming, but tries to cater to the casual audience as well?

NES Versus PC Engine and Sega Master System;, Gameboy Versus PC Express and Atari Jaguar, Gameboy Color versus Neo Geo Pocket Color, Gameboy Advance Versus N-Gage, DS ( all iterations) versus PSP, Wii Versus 360 and Playstation 3, 3DS versus Vita and IOS, and Android Devices, Wii U versus Orbis and Durango.  In all those instances Nintendo had the inferior technology.

The only times they've had comparable or better technology were Super Nintendo ( lacked external CD-Rom Drive), N64 ( lacked CD-Rom Drive)  Gamecube ( lacked DVD).

NES Versus PC Engine and Sega Master System;, Gameboy Versus PC Express and Atari Jaguar, Gameboy Color versus Neo Geo Pocket Color, Gameboy Advance Versus N-Gage, DS ( all iterations) versus PSP, Wii Versus 360 and Playstation 3, 3DS versus Vita and IOS, and Android Devices, Wii U versus Orbis and Durango.  In all those instances Nintendo had the inferior technology.

The only times they've had comparable or better technology were Super Nintendo ( lacked external CD-Rom Drive), N64 ( lacked CD-Rom Drive)  Gamecube ( lacked DVD).

Motion Control proved to be popular for Wii during that time, but once Kinect released, it took away the only ace in the hole the Wii had, so you see it being the first console of its time ( not of its Gen there's a difference) to die off despite its early sales.  So comparing Wii U and Wii that way is like comparing apples and oranges.  Really the closest analogues to Wii U are Dreamcast, Xbox 1 ( during the time when it was called "Portbox" by detractors as Wii U will mainly be getting slightly spiffier ( if they manage to turn out better than Arkham City) ports from PS3 and 360 prior to the release of the Next Gen consoles) or maybe the Gamecube if it had been released a year earlier ( though the horsepower difference between Wii U and the Next Gen consoles will be more like the difference between 360 / PS3 and Wii than it was during the 6th Gen).

Yeah I know, its like if they make one kinda like the Wii U.............O.o