Today “viable for gaming” seems close to equivalent to “can passthrough secondary GPU to a gaming VM”, but it has constraints (eg. output to separate display, or get video stream back to dom0 through other means like VNC), and that GPU cannot be used by programs in different VMs.
When sys-gui-gpu is made to work for more hardware, and when a GL/VK command-streaming infrastructure is put in place, I hope it will be much more comfortable. More manpower and neurons welcome 