I've also wanted to do this for a while, but there were always a few too many barriers to actually spin up the project. Here's just a brain dump of things I've seen recently.
vGPUs continue to be behind a license. But there is now vgpu_unlock.
Turning VMs on and off isn't as slick as either of the above, but that is doable today. You'll just have to build all the switching automation yourself. That could just be a shell script running QEMU/libvirt commands, at a minimum.