Mario and Zelda are necessary to Nintendo's survival, not just new IP's. The Wii U hasn't even had it's Zelda yet and it's looking to get it the moment it is dead. The third party support issue came about because of the systems hardware not being up to snuff, meaning they couldn't port games over easily. The NX should remedy a lot of this and hopefully after successes like with Splatoon, we can see a few new interesting IP's show up.
That's partially true. But many games were still made for the PS3 and 360 up until recently. The reason 3rd parties stopped or didn't even start releasing their games on the Wii U is simply because 3rd party games don't sell on the Wii U. It's been a progressive trend since the N64. Fewer and fewer publishers/developers take a chance on releasing their titles on Nintendo systems because they are seeing diminishing returns.
Nintendo planning to launch a new console three years into the current cycle is tantamount to retail suicide, especially with the PS4 selling as fantastically as it is.
I'll end up buying the NX or whatever because I do love Nintendo games. But let's be realistic..I"m going to put it out their right now. The NX will sell about the same as the Wii U, maybe a little better. And that's it. Nintendo hasn't learned from their past mistakes. Hell, they still can't even get their user accounts on the same page. I have to download my Super Smash Wii U characters, then enter a stupid code on the 3DS or vice versa to download them there! It's ridiculous. 
That's most of it. The other part is the fact that, and someone correct me if I'm wrong, UE is not natively compatible with the Wii U, the folks working on the Bloodstained port are the first people to go all in on trying to get UE running on Wii U.
I'll just throw a similar situation in there. The Virtual boy was released before the N64, it failed so fast and so hard. Then they released the N64. At the time, folks were saying the same thing about Nintendo, talking about how stupid they were to make the [Wii U/Virtual Boy] and that they are going to go out of business doing this stuff like releasing a new console like [NX/N64] so soon. Will the NX turn things around and put them on top? Of course not, but it's a step in the right direction. Despite what Soera will say, the N64 definitely helped Nintendo recover after the Virtual Boy.
It is true though, Nintendo's hardware has been consistently behind the curve for the past 20 years. But despite what folks are saying, Nintendo is posting profits.
