Valve has been doing amazing things in this space, but for now my understanding is that it's more of a "most games will work pretty well" scenario, which is not really what I want for my primary games machine.
As another comment points out, its called VFIO. From that subreddit: "VFIO stands for Virtual Function I/O. VFIO is a device driver that is used to assign devices to virtual machines. One of the most common uses of vfio is setting up a virtual machine with full access to a dedicated GPU. This enables near-bare-metal gaming performance in a Windows VM, offering a great alternative to dual-booting"
I haven't worked in windows space in awhile though, and state changes rapidly, so there may be other options now that utilize a single GPU across host and vm without losing performance.