I've been thinking about this a bit too...
First off, Nintendo's on the right track, the implementation is just off a bit. The Wii was a success because it was cheap enough to be a contender as an impulse buy, but it was also fun and accessible- so it
was an impulse buy compared to the 360 and certainly the PS3. The DS was in a similar position against the PSP, and the 3DS is essentially running of the DS's success (and 3D).
The Wii U is not that. Its not an impulse buy at $350. And its not instantly accessable; Wii Sports instantly conveyed what was fun about the Wii- Nintendoland does not do the same for Wii U. But the real hindrances are the price, and the fact games are absent. I see people trying out the Wii U all the time in Walmart (unlike the GC). Something is keeping these people from buying it, its either the price or the fact there are no games for it. Hell, that kept me from buying it until I could pair a new $264 Basic set with a $40 260 GB WD My Book on Ebay, and my family's owned every Nintendo system since the SNES (unfortunately I got the Wii U before the price drop, but I still did better considering the premium only comes with 32GB).
For Nintendo's next console, they can do better. Here's how.
1) Make a full break with the previous Wii hardware and improve on it.
Nintendo messed up the original Wii implementation by not including WM+ from the jump. This split the userbase and WM+ caused other problems with the Wiimote add-on not being as good as the built in WM+ (Zelda SW proves this). Nintendo should drop the Wii-mote design altogether and opt for a Wii-mote implementation like Sony's (the remote broadcasts the IR info instead of the sensor bar broadcasting IR). Sony's implementation was more accurate and should be copied. Don't worry Nintendo, we know you invented it in the first place. Also, add a fucking click stick to the nunchuck for God's sake (COD Black Ops is driving me crazy on Wii U because of this).
The Wii U's Gamepad is basically fine, I think. It may not require a full break, although the N7's (Nintendo's 7th console) Gamepad should be sleeker.
2) Don't be afraid of splitting the userbase. Lower the price of controllers.
Alot of people are arguing for the Gamepad to be dropped from the WiiU because it's increasing the price of the console. I disagree with that. Nintendo can't do that for the Wii U because there's litterally no reason to buy it after that other than for Nintendo games (GC). The N7 need not be burdened by such logic. The console should be focused on being as powerful as it can possibly be at $300 midway through the X1 and PS4 generation. It should essentially copy Sony's fantasic hardware design, only be more powerful- Sony may have out Gamecubed the Gamecube, so copy them again. Also, include a small (50GB) SSD with a few GB dedicated to a developer chache. Even if the N7 had the exact same processor as the PS4, the SSD would help propel it alot further.
What was this section about again? Oh yeah controllers. The only way you're going to undercut Sony, and X1 mid gen on value is through
not having a pricey controller. The hardware is going to be too expensive. Therefore, the consumer should only get one controller per console. They one they get should be up to them (Wiimote, Gamepad, or Classic). Sell the consoles separate from the controllers, and simply allow the consumer to select a controller from the store at the store counter. The (new) Wiimote and Classic come free with their console purchase, and the discounted Gamepad costs them $10 extra (normally $25). As a secondary controller purchase, the Wiimote and Classic controller prices are dropped to the floor (sold at production cost + shipping + storage) and shouldn't cost more than $15 or so. As I said, the Gamepad would cost $25 as a secondary controller, because it's more expensive to produce.
[edit: The Nintendo Eye or whatever is used to run the new Wiimote is included as well (as is the case with the Wii U), it shouldn't cost too much because its basically a camera].
The reason for doing this is to de-couple the Gamepad cost from the console's cost (the problem now with the Wii U). Since the Wii U Gamepad will be compatible with N7, early adopters won't demand so many- lowering costs for Nintendo greatly.
Arguments against this are that it will split the userbase. This is NOT true. Developers are still using the Wiimote even though its not included with the Wii U (and not even really advertised anymore). Activision still uses it in COD. Nintendo uses it in Pikmin. There are likely other games I'm forgetting about. Developers don't seem to mind developing for alternate control schemes. Programming controls is actually pretty easy. One could also argue that its wrong to FORCE controls on the consumer. The consumer should be free to select which controls they want to use. They also shouldn't be forced to subsidize controls they don't want to use- as Nintendo is currently doing.
Making the controllers cheap, and optional appeals to the widest variety of consumers.
Why do you think there are so many versions of spaghetti sauce?
[edit again: Also make the next Gameboy/DS thing fully compatible with the N7 as a Gamepad. There is NO reason not to do this, all it would probably take is another radio within the next handheld. Nintendo's full product line should be 100% compatible control wise next time around. Remote play of N7 games through the Gameboy, "Super Gameboy" style TV play, the whole shebang. They should even consider some game cross-compatibility]
3) Use indies to sell the console and the controllers.
So we've got cheap ($300). We've got unique (controllers). Now we need fun. That's up to the games, of course. That's where indies come in. Before the console is launched, Nintendo should release a virtual devkit to indies (a power profile) so they can begin programming to the relative specs of the system. Of course, these pre-specs would be vastly underrated, so the system can run the optimized code at launch. Nintendo should start a competition with the release of the dev kit (a year or earlier before launch) to allow indies to develop an equivalent to Wii Sports for the N7 using Mii's. The best 5 games in the competition get put in the compilation. Requirements being that all the games use either the Wiimote or the Gamepad (Classic controller is optional) and be multiplayer. For incentive, each game that gets selected earns a million dollar cash prize from Nintendo ($5 million in total prizes). The game would come packed in with the system... and the $5 million dollar cost to develop it written off as sunk.
This way, Nitnendo doesn't have to spend time writing much of its own time developing a Wii Sports. The end result from indies would likely be more creative anyway. The competition could even be held anually, essentially creating a new Nintendo "franchise" that can't be easily copied by Sony or Microsoft (lest they radically change direction).
I have other thoughts on this, but I'm tired of writing. That's the jhist of what I think.