Absolutely nothing. While there are a couple of interesting games on the Xbox (namely Quantum Break, and Quantum Break), I would rather not buy two consoles again as I feel I won't get a return from my purchase, nor I am willing to pay for online subscription twice.
I also am no fan of Microsoft's willingness to share information with NSA. After all, they directly assisted NSA to bypass security for Outlook and Skydrive. Given the recent exchanges between the two firms, I don't expect things to be entirely rosy with the always on Kinect.
I'm just going to stick with the combo of PS4 + PC. Money will be better spent on a beefy GPU. Furthermore, Sony have a long history of releasing quality games right to the very end of the console. Shadow of the Colossus, God Of War 2, The Last of Us, Beyond Two Souls, Gran Turismo 6.