My take on this? Microsoft should have had backwards compatibility from day one. It was possible but the company just didn't want to implement it. I believe sales of the Xbox One suffered because of it.
One nice feature on Xbox One is backwards compatibility support for Xbox 360 games (and original Xbox games soon). If you own older titles on-disc or digitally, you can play a growing list of these on Xbox One at no extra cost, which is a pretty nice option to have. Even if you don't use it all that often, it's nice to know it's there.
