LinusTechTips did something similar to this using unRAID, which is basically the Linux equivalent of FreeNAS, using KVM for virtual machines. They got 7 people all using independent monitor/keyboard/mouse & dedicated graphics card running off one machine.
The basic idea was this -
Create a VM from each user
Pass a dedicated PCI graphics card through to the user's VM.
Plug the user's monitor into that graphics card
Plug in a usb keyboard/mouse for that user
Pass those two devices through to the same VM
I'm not sure if there are any pci-passthrough problems with bhyve Windows guest at the moment (I'm sure I've heard some people having problems), but if there aren't you should be able to pass a dedicated video card through to a VM. It will then show up in the Windows guest as a local device and you can install the nvidia/amd drivers. You end up with the base system outputting via on-board graphics, and the VM outputting to a second monitor plugged into the video card. You should also get audio if using HDMI as this is handled by audio hardware on the GPU.
The problem would be the keyboard & mouse. bhyve doesn't have USB passthrough yet to be able to give a keyboard and mouse to the Windows machine. The only way to connect to a bhyve Windows VM with keyboard/mouse control is RDP. We should have UEFI graphics soon (...) but that would also be fairly useless for anything other than basic graphics.
Dual booting or two disks would be a lot easier.
