I've seen things where you have multiple video cards and can use one gpu to render to a framebuffer which is transferred to the other video card to output. I'm sure it adds latency, and it's probably unsupported... But no output doesn't mean can't do gaming... It just means gaming will be iffy.

There's some virtualized desktop server stuff too. Run a bunch of desktop sessions on a beefy computer and send a video stream to desktop players. With the right codec settings, the latency is probably ok for many games.