Let's look at the last 16 years of Nintendo's history, what have been it's greatest successes? The Wii, the DS and arguably now that sales have taken off, the 3DS. What do these platforms have in common? A great gimmick and a low price. The Wii is the least technologically advanced console of this gen by a wide margin, but thanks to being the first company to put motion controls in the mainstream and also being the cheapest console of the 3, it's leading in marketshare. The DS was well behind the PSP in power, but also well behind in price and it sported dual screens, something brand new to gaming, so it's achieved well over double the sales the PSP achieved. The 3DS is also lacking in the power department, especially when compared to it's closest rival, but it's also got 3D without glasses - a great gimmick, and after the massive $80 price cut, a low price. 

What happens when a Nintendo console doesn't have a great gimmick and a low price? Well, Nintendo 64 and Gamecube happened, selling just over 50 million units combined; not terrible, but that's nothing compared to what any current gen console has accomplished. I think the Wii U will go down the same road. If the Wii U is going to be similar to Durango and Orbis in terms of hardware capabilities, then it loses the first major selling point it needs, the low price. Now, the Wii U does have one major feature seperating it from the other 2 consoles, the tablet controller, but it won't be enough. Motion controls were brand new when the Wii came out, dual screens were brand new when the DS came out and 3D without glasses was brand new when the 3DS came out. Tablet gaming, however, is something casuals have been doing for the last 4 years, and it's only going to get bigger. The Wii U's gimmick isn't anything new, it isn't as innovative as it's predecessors gimmick, so the Wii U loses the second major selling point of Nintendos greatest successes.

What if Nintendo go for a low price point for the Wii U? Now it not only has a gimmick that won't move units, but it's also lacking third party support. It has only it's first party software and die-hard Nintendo fans to rely on, and there are only so many Rolstoppables and NintendoPies out there, enough to make the Wii U a decent success, but not enough to truly compete with rival platforms. 

Summary: 

Low price = less power = no 3rd party support aswell as lackluster gimmick

High price = more power = loses major selling point of Ninty systems aswell as having a lackluster gimmick, bad sales could possibly lead to the loss of 3rd party support aswell

Am I missing something? And I wrong about the tablet controller? I'd like to hear your opinions.

You're missing Gamboy, Gameboy Advance NES, SNES all best selling systems in their times.

The only thing I agree with in you argument is the price point, Nintendo should have a lower price point than competitors, because undeniably a large share of Nintendo the userbase is made by kids.
Do you really think 3DS is selling well because of 3D? :/

I am offended that you mentioned RolStoppable and Nintendo Pie, but not me.

As much as I don't like some of the direction that Nintendo is taking with the Wii U, there is no way that I could see it coming in 3rd because some else will screw up worse. I'm assuming that you have seen the Vita and 360's recent sales...

By the time the next XBox and PS release, Nintendo will have the lowest price, so there goes your first argument.

Concerning your second point. The Wii U pad is not just a controller sporting a touchscreen. The possibilities far exceed those of the NDS or 3DS. It's not just 2 seperate screens for one person. The screens can interact with each other. The screens can be distributed to different people. New Asymmetric Multiplayer possibilities. New options for party games etc. etc. Whatever small the gimmick of this Controller may be to you (I think its huge), its a helluvalot bigger than the fourth itteration of the dualshock controller.

The power of the tablet gimmick really depends on the software for it. E3 wil the showcase for that.

I think the WiiU will take 1st place next gen, assuming that it receives support comparable to that of the 3DS

they should not have a lower price point because when ps4 and xbox8 are out the price will go down and sales will go up for the wii u..look at the first two years of the xbox360 the PS2 outsold it every month

"Low price = less power = no 3rd party support aswell as lackluster gimmick"

Indeed, just like the PS1 and PS2 didn't get 3rd party support because they were the least powerful.

Fact is, we know nothing about the PS4 and 720, so judging now is stupid.

The Wii U will have a low price though. I guarantee it will launch at no more than $300. Nintendo might even take a small loss on each one for the first year or two.
The gimmick like you said is the Tablet controller. It doesn't necessaritly have to be NEW to sell systems. All it has to do is WORK and be innovative.

Nintendo 64 and Gamecube had arguably the best Nintendo games of all time, yet they are the least successful Nintendo consoles from a marketshare and sales standpoint.