Yeah, would this be feasible for first person shooters where every millisecond counts?

If this added even a single millisecond I'd be extremely surprised. I can guarantee any latency this adds is imperceptible.

Most laptops with discrete GPUs don’t have a direct connection to the display. They copy the frame buffer back to the integrated GPU’s frame buffer and then send it to the display.

When that display is a VR headset the latency is very real and it’s a big problem. Only in the last year or two has the hardware started to change.

I would be shocked if this didn’t add latency. It’s just a matter of how much.