Windows Central shared some notes from leaked documents pertaining to a developer event. If those are anything to go by, it looks like Microsoft is stipulating a limit of one keyboard and mouse to be supported per console (while several gamepads can be used at once).
Next, developers will be able to detect the presence of a connected mouse and keyboard, and are encouraged to use that factor for matching up players in competitive titles so that those using gamepads aren’t at a disadvantage. Plus, all USB mice and keyboards that work on Windows should work on the Xbox – but wireless gear and those that use custom dongles may not.
Adding support for these peripherals would allow Xbox owners to try a wider range of games that require numerous key bindings, like strategy titles. This could also make it easier for PC gamers to transition smoothly to Microsoft’s console, and allow console veterans to try out new playing styles since they won’t be restricted to traditional controllers.