During the Tokyo Game Show, Microsoft's Albert Penello confirmed to Gamespot that the Xbox One's HDMI input port would work with any device, including its main competitor: the PlayStation 4.
A post over on NeoGAF sees Penello explain by saying it "won't be a great experience," where he said that HDMI latency will affect interactive content. We should expect more details in the coming weeks, but the HDMI input will provide more lag if you use the PS4. I don't see why you would do that, as most TVs and amplifiers have multiple HDMI ports.
Microsoft most likely provided an HDMI input port for the use of cable/satellite TV boxes, so you can plug it directly into the Xbox One.