It would be an optional feature of course. Most people that can't afford a 3D TV now, may get one by the time the generation is up in 6 years. They cost almost the same as regular new TV's. The new passive ones are much more practical with glasses being included and really cheap. If you don't like 3D or don't have it, don't turn it on.
The 3Ds is a tiny portable single player system. It's good for playing by myself. But if I invest in a TV, I want it for multiplayer experiences. My 24" monitor is fine for playing by myself in my bedroom. Trying to do split screen and parties on it is not good. I want the big TV for when I have people over.
And they do need 3D to be nextgen in the eyes of the core gamers. The Wii U is barely more powerful than the 360/PS3. I think it's about the games and not the power, but I like the WiiU, but if you want to convince the core gamers, it needs 3D and better online functionality.
Nintendo already knows how to render the games in 3D with the 3DS. It would take what, maybe a week or two of work to make the new Wii U games work with 3D.
Older active shutter 3D sucked, but the new generation of Theater3D technology, with the passive glasses and no dimming, is incredible. If they expect us to pay $60 per game, we should get something more.