The problem with the display itself is that the optic lenses surrounding the rift curve the display to the extents of your vision. It's not like you're seeing a screen really up close, it's like the screen is surrounding your eyeballs (to a degree).
The actual display on these devices is just normal screen, usually a cell phone screen running in landscape orientation (read: software rotated). As an example, if you connect your rift to a PC and aren't running a rift game, you can pop off the lenses and look at the screen inside, and it's just a normal computer monitor:
Now, the problem with viewing non-VR adjusted images on a VR display is that A) the image is 1 single screen displayed across two eyes, so you see half of the image on your left eye and half of the image on your right eye. Our brains aren't wired to take in imagery like this, so it winds up being slightly physically painful and we can't make sense of what we see at all. And B) the image is distorted around your peripheral, and the fovea of the lenses makes it so only the center has any sort of clarity.
Now, there are tons of programs that will, as an example, render the screen to a floating window in VR space, like so:
Once again, without the lenses, you simply see something like this:
Now, the rift DK2 has a very special undocumented feature that not many know about. If you drive a DK2 at 120 hz (the DK2 normally operates at 70 hz) if enters a special mirroring mode where the display naturally doubles up. This is
desktop mode and each view port will display the entire desktop scaled down. Many thought nvidia's drivers were fucked when using the rift - in actuality, it was Nvidia's 3DTV drivers that were driving the rift at 120 hz causing mirroring mode.
TL;DR: what you describe isn't only possible, it's a major selling point of these devices. VR movie theaters are huge on gear VR: