Well, we already know it will live until 2017, that makes its lifespan 5 years, the same as the N64. Now tell me that was a sucky console, I dare you!
But seriously, from many posts it would seem people base its age as an indication of its quality. Let's not forget so many other generation that haven't lasted the 8 years that last-gen did.
I see lots of hate for the Wii U, but this thread gives me an idea. People seem to want to compare it with the PS4 and Xbox One. That's just futile.
Personally, I see Wii U as going parallel to those consoles, but not in the same battlefield. I know I'll buy a PS4 and I wasn't interested in the Wii U until I played it. Now I see it and my future PS4 as complementing each other; much the same way I don't ever think PC or PS4, but PC and PS4.
The reason for this? Only a few games coming out for either console are the same - certainly less so than the shared titles between PS4 and Xbox One - and with perfect sense: they're not technologically equivalent.
The Wii U, like the before it in its generation, has much lower hardware specs, but Nintendo makes up for it giving you a very different experience. In the Wii, I wasn't interested in that experience in the least, also not when Microsoft and Sony copied it. But in the Wii U it comes with variety (such as the many different available controllers and how many games use them differently), but also with Nintendo's most obvious and biggest advantage, which is their exclusive IP.
At least to those of us who grew up on the NES/SNES/N64 there's nothing quite like Pokemon, like Zelda, like Mario. It's as easy as to think of modern-day platformers... you have indie games like Super Meat Boy or Braid, or you have the latest Mario game. The particular mix of action, adventure and RPG from Zelda? There's lots of amazing, epic, adventurous RPGs but none give you quite the same feel. Smash Bros? There's no fighting game like it.
That said, if the NX can get on par with the others in hardware - and let's face it, with a 3-year advantage they could even improve upon it - they could not only take advantage of the market for all current triple A console game franchises (Assassin's Creed, Tom Clancy, Call of Duty, Battlefield, etc...) but also have the edge with their exclusives. It could go from the other console that you own to the one you're aiming for, your gaming priority.
So with that, let's enjoy the Wii U for what it is (or not, it's your choice but I have made mine) and hope the Nintendo NX kicks some ass!