Actually I was talking about the general ability to plug a PS4 into an Xbox, the fact people needed confirmation on it is head scratch worthy. The better question would be why WOULDN'T it work? MS already stated how HDMI In works so it doesn't take much to figure out hey...this would apply to PS4 or anything with HDMI out really. Unless Albert misspoke and it's still HDMI in or Xbox One and not concurrently.
If anything the real take away is you no longer have to switch between your HDMI In'ed device (Cable TV being the main selling point) and Xbox like they showed during the reveal, but rather you can you can use them side by side. Which means they've done some work on their OS and how it handles multiple applications of various size and nature.
I agree...yes it was obvious that the PS4 should work with the xbox one but it wasn't obvious that the PS4 could be played in snap mode while you play the xbox one at the same time. Thats what I took from what Albert said. Maybe I took what he said the wrong way but if you can play both at the same time in snap mode....this would be cool and is not old news.