Now :
Speculation time!
When you'll slide the Switch in the VR helmet, there'll be a 2nd non opaque
cheap LCD screen already in the headset. Both of them will work together to create Cascading display.
Nvidia created this before
https://www.youtube.com/watch?v=0XwaARRMbSA&feature=youtu.be
With their algorithms and the use of 2 cheap LCD displays, they can reach the illusion of having 4x the resolution.
If people weren't so dense, this would have been quoted a hundred times in this thread already rather than all these "lol VR with 720p screens? Okay...." type posts.
Not only is this Nvidia, who Nintendo already have a big partnership with for this console, but they demonstrate how they were able to get these results with 2 off-the-shelf LCD displays. I think they say in the video that they just removed the backlight from one display and arranged the panel in a way that made it "cascaded. Sounds super cheap to get the desired effect. I'm surprised no VR HMDs go for this approach considering how expensive additive higher resolution displays, how much more energy they must use, and and how much more power it takes to push that many pixels.
It also sounds like having cascaded displays allow for a smoother framerate that appears faster at lower refresh levels simply by staggering refresh frames. That seems like another benefit Nintendo could use with this technique for smoother video output for VR at a lower actual display refresh rate.
If they add a magnetometer like the Wii U Gamepad (assuming there is nothing like that inside already) to the HMD, they have another sensor for positional tracking and then you have a headset that is at least on par with the GearVR (as it seems, from the Switch patents, that the core device has gyros and accelerometers already built in). Even without a magetometer, it would be on par with the Google Daydream with seems to rely soley on the phones' gyro and accelerometers. Speaking of the Daydream, the Joycon are better than the Daydream's sole controller in that they have more buttons, there are 2 of them (one for each hand), and they have haptic feedback built in. Already that makes the Switch compatible with 2 of the lower cost, larger install bases for VR software, and maybe can even bridge the gap enough to get some game support for at least some of the other higher end game support (let's be for real, roomscale will not be the standard going forward, and basically every headset supports standing/sitting/turning experiences).
On top of that, they could have the Switch "dock" in the HMD to be able to get higher performance out of the machine for the extra power that would be needed and it already had a fan built in so it doesn't overheat, which is more of a problem for smartphone mounted designs.
I think there may be a real possibility Nintendo already knows they can pull it off with the tech they already have in the Switch, but like Kimishima says, comfort is a real concern that developers are still struggling with overcoming in multiple areas, especially when it comes to incorporating traditional gaming. I mean, it seems they know of the common technical/software/hardware issues that can cause discomfort, but when it comes to movement in ways that may seem normal but causes a certain "uncanny valley" sensation, it can really mess with some people in some circumstances.