Using Windows 8 on the Xbox One is most likely better than installing a limited, unstable, or outdated operating system on the One since the One and 8 both benefit from the latest updates, service packs, patches, and optimizations which the Windows staff made for 8.
Although, you can't play Highend PC games or use Desktop programs on the Xbox One. The Xbox One would most have access to the Windows 8 App store which has a lot of Windows 8 Game Apps, Information Apps like Wikipedia, RSS news reader, and other types of apps for using on the TV. There is also a possibility for Xbox One to unlock some of the PC features of Xbox One like a Xbox One version of MS Office which include Word, Excel, Powerpoint, Outlook, and Access, so you can work access documents like game walkthroughs from a .Doc word file, make a spreadsheet of your achievements, or item lists for a game you are playing, make a presentation about a game, access your email, and make a Access database file to keep track of your virtual gaming items, and characters for a game.
The Kinect is not just a motion controller. It is also a highend HD webcam, and microphone, so you can use it for Skype, so if you need a PC to video chat with someone it is an added value for people who use Skype, and videochat apps.
The Kinect will also have PC support, so you can use it as a webcam, or motion controller on a PC if you want to according to
http://www.develop-online.net/news/44273/Kinect-2-support-coming-to-PC