Is that finally ready to go (I haven't been able to check out the links)? That's been basically known to people who follow game dev news that it was an upcoming feature since a little before the console launched, it's just been nothing but a promise up to this point.
If it's finally released, awesome. That's a major reason why I decided to get an Xbox One over PS4. I made games with XNA on the previous system, so I'm excited to finally get to start developing on the Xbox One.
Looks like Unity is the engine Microsoft picked this go around to support Xbox One development. Maybe XNA will be resurrected at some point, but I doubt it will be anytime soon.
XNA was nice and fun to program with, but I think Unity is generally a better game engine, it's still C#/.NET development, the base version of Unity is pretty open and free now, and you're not locked into "The Microsoft Platform" with it.
So overall I'm pretty satisfied. I could probably even quickly port some of the XNA code over with minimal changes (not the graphics, unfortunately. Assumed a fixed size 2D viewport for all my layout and animation code, which was a mistake).
If it's finally released, awesome. That's a major reason why I decided to get an Xbox One over PS4. I made games with XNA on the previous system, so I'm excited to finally get to start developing on the Xbox One.