https://www.gamespot.com/articles/microsoft-talks-xbox-one-keyboard-and-mouse-suppor/1100-6456853/

While the Xbox One does not have an official, Microsoft-approved plan for support keyboard and mouse controls (at least not yet), there are ways to do it. One way is through the use of adapters. Microsoft is apparently aware of this, but the company is not taking action in the case of multiplayer shooters--where keyboard and mouse players would theoretically have an advantage.

The reason? According to Xbox engineering lead Mike Ybarra, Microsoft could block keyboard and mouse setups on console, but won't do it because the company wants to give developers the freedom to operate their games as they see fit. Not only that, but a keyboard and mouse setup can be a helpful solution for players with accessibility considerations.