This is something I thought of when the console was first announced. It's likely that Nintendo was considering VR while designing the Switch, and while it's also likely that the existing hardware might not make for a particularly good VR experience, due to the device's size, weight and resolution, they could definitely make it happen in a "Switch Lite" with a 1080p screen released as a half-generation update.
Jeff Fx :
It wouldn't even have the high quality 3DOF tracking that cell phone VR does
The joy-cons each include 3DOF tracking, so one of them could attach to the headset to fulfill that role. One of them includes an IR camera as well, which could be used in combination with an IR emitter (like the Wii's sensor bar) to also add positional tracking. And of course, there's also the possibility of them incorporating additional electronics into the headset peripheral itself, or an external camera sensor like the Oculus Rift uses.