Placing amiibo at the heart of the new system would be a massive mistake. The great thing about amiibo right now is for Nintendo fans like me who hate toys and plastic tat they're still easily ignorable, yet those that DO like them are still getting a bit of value out of them.
Make them a key feature and you're only shrinking your audience, imo.
It's impossible to properly speculate what 'mass-market appeal software' they'll go with this time in the vein of Wii Sports and Nintendoland until we know what the major input of the console is (touch / standard controller / motion etc), but if I was them I'd look at the lessons of Wii Sports. One of the huge reasons that that sold so well was because it was clean and antiseptic. Felt designed for anyone, not just gamers. The idea of playing sports is society-wide. My folks would play a game like that. The idea of going on an adventure as an elf in a green hat? Not so much. Not sure if they'll try and recapture that audience again but if they do removing Nintendo mascots and making the whole thing (outside of the gameplay) as bland as possible will be pretty important.
As for the hardware, what I'd love to see them do is two SKUs with the handheld from the start. A cheaper one for kids (think what the 2DS is to the 3DS, but without the horrible design) and a better version for their hardcore fans, with a higher screen resolution, better battery life and better industrial design. Let's say the kid's version came in at $150, there are plenty of grown Nintendo fans like me who'd happily shell out $300 for those features.
Shit, I'd shell out an extra $150 just for an industrial design that doesn't make the system look like a child's toy. The dangers of confusing the market (or making the lesser SKU look like a consolation prize) are probably too great though. Still, it's nice to dream.
On the Wii U, I think it's a system with a very desirable library but on a system with a serious image problem.
The name is confusing, but it's also bad. Despite being a big fan it's still embarrassing to say. It carries the negative connotations of the Wii but not to the audience that loved the Wii.
The console was gimmped for dumb reasons like low power consumption which appeals to basically no one.
When it launched it received a lot of poor ports of multiplatform games where the system rarely came on top of the PS360 so it was more expensive and less powerful than those old systems in the eyes of consumers.
Then several games that even the Wii got were skipping the system. Nintendo fan sites reporting "this game is coming to PS3 and 360 but not Wii U" over and over again which crushed the spirits of those that supported it over time.
Then bad news came resulting in lower sales which result in bad news which resulted in lower sales. It's a cycle that ate away at any good will the system could muster.
All this combined with bad marketing at the start to no marketing later on.
3DS hurt the system too. Despite its issues, the huge price cut managed to turn the system around in the public eye. All the previously mentioned issues made it undeniable to even some Nintendo fans. With the 3DS having some Wii U equivalents (NSMB2, which also sparked a Mario fatigue) a lot of them were more than happy to just stick with that for Nintendo's library.
So yeah, I think the system could've found more success if Nintendo was more proactive towards the start but I just hope that they take this as lesson and make sure to push the next systems well with more appealing names, better marketing, etc.
The Wii U's fate was sealed long before it ever reached store shelves. When devs and publishers saw the gamepad, they quite rightly guessed that it wouldn't have the same impact as the Wiimote. Thus they just put a couple of port teams on the machine 'just in case', while they worked away at their core PS360 bread and butter. Then the second those devs and publishers saw what Sony and MS had cooking in comparison to the weak shit Nintendo was bringing out they bailed immediately, and as you saw it was clear right after launch that they had done so. Those MS/Sony meetings would have been well before Wii U's launch, after all.
So many terrible decisions by Nintendo. If they go 'low power consumption' again I will pull my hair out. No one gives a shit.