I don't have solid numbers, but a quick Googling suggests the rate of desktop deployments of Linux is under 2%, and VR-ready deployments is going to be a thin slice of any desktop OS deployment (I have no reason to believe Linux users are more likely to have a VR rig attached to their machine than average, and I'd put money on it being actually less likely unless they have a machine configured to dual-boot).
I don't have solid numbers, but a quick Googling suggests the rate of desktop deployments of Linux is under 2%, and VR-ready deployments is going to be a thin slice of any desktop OS deployment (I have no reason to believe Linux users are more likely to have a VR rig attached to their machine than average, and I'd put money on it being actually less likely unless they have a machine configured to dual-boot).