Well I don't believe the 3DS will flop for being 3D but because you now have a generation of kids and parents who are use to cheap, instant download quality games on the iPhone and increasingly Android.
Ask any school kid if they want an iPhone or Gameboy and they'll answer iPhone. For parents, it's a dream come true because it means no longer having to buy 1 or 2 games at $80 a pop.
When Nintendo doesn't even sell 5 million handheld consoles in the first year (my prediction), the 3D industry will self destruct and it'll have a trickle-on effect for other devices including TV's and movies (remember, the video game industry is much bigger than the movie industry).
After years of worrying about Sony, Sega & Microsoft, who would've thought it would be Apple to knock the lot off the top spot.
Sorry for getting a little bit OT.
interesting comment = "the 3D industry will self destruct" - I take it you meant certain products that do or could implement 3D viewing technology, like a Gamboy? 3D Viewing technology can only grow in my opinion so it is just a matter of which devices that have 3D viewing capability become the most popularly accepted. Your example about the Smartphone versus a Gameboy is somewhat valid ... today that is, we don't know if for example a Gameboy of tomorrow may or may not incorporate a phone. In any case 3D Smartphones, or more correctly Smartphones with 3D capability, both viewing in 3D (without glasses) and incorporating a 3D Camera have now been released.
Smartphones (iPhone, Androids) are no longer phones, they are mobile communication, data and entertainment "Devices" which will from this point on incorporate 3D capabilities. So regardless of what devices may be developed in the future it is not likely that they will not be 3D capable. Just as Smartphones are impacting to some degree on other devices like Gameboys, Digital Cameras and even Notebooks to a lesser degree they are also expanding the use of 3D technology at the same rate as the advancement of the use of Smartphones - every Smartphone will have 3D capability within a year ( if not by the end of the week

).
3D Games will become HUGE - as it was rightly pointed out in this thread the Games industry far outstrips the Movie industry, the determining factor in the success of 3D viewing will come primarily from games and not movies. When 3D Computer screens (without the need for glasses) become the norm within a few years (they are already available in Desktop and Laptop from a few manufacturers however they are still embryonic) then 3D Games will become the norm, whether dowloaded free or rented online or purchased is neither here nor there as far as the sustainability of 3D viewing is concerned.
Smartphones, likely to be called by some other name down the track as the phone component becomes incidental (SmartDevice is being bandied around as a frontrunner) will make 3D a success - it is already happening.
3DTV will survive but will take a long time to become the norm, if inded at all but that is of little consequence as Television is no longer the prime entertainment media, mobile phones are
So hopefully some of my stable of 3D mobile and computer monitor domains will bear fruit soon (3DSmartphones, 3DMonitors, 3DPCScreens etc.)
cheers,
Shags