ASRock is preparing 8-series Haswell motherboards with built-in HDMI switching. The option lets you pipe in a secondary HDMI feed even if you have limited monitor inputs. It even works when the system is powered off, but the hotkey-powered switching takes about five seconds to complete. It seems ASRock is really trying to differentiate itself with its upcoming motherboards as selected ASRock boards will feature a waterproof coating as well.
While the video doesn't really show whether the HDMI input adds any latency, it's clear that the monitor is connected to the motherboard's display output. There isn't a graphics card in sight. Presumably, running your PC's output through the motherboard is essential to the switching mechanism. That doesn't necessarily mean you're restricted to integrated graphics, though—Lucid's Virtu software allows discrete graphics output to be fed through the mobo.
Platform integration has made it increasingly difficult for motherboard makers to differentiate their products, but ASRock clearly has some novel ideas up its sleeve. My fingers are crossed for a video of the waterproof coating in action. I'm not sure that's something I want to try for myself in the lab - source tech report.