Xbox One being able to play Xbox 360 games is something a lot of folks want to see, and Microsoft is definitely looking into it. With Build having just taken place in California you can bet that the question came up in one of the sessions. It was put to Partner Development lead, Frank Savage, by a member of the audience, and garnered this response:
"There are, but we’re not done thinking them through yet, unfortunately. It turns out to be hard to emulate the PowerPC stuff on the X86 stuff. So there’s nothing to announce, but I would love to see it myself."
What form any emulator would take is still open for debate, though simply sticking your discs in might not be the way it would work. In any case, it's great news that Microsoft is at least looking into making it happen. Whether it will or not is another story for another day.