Mouse and keyboard support has been on the cards for quite a while, and it's drawing ever closer. Minecraft's "Better Together" beta already supports mouse and keyboard inputs to some degree, owing to Universal Windows Platform (UWP) APIs that function across all Windows 10 devices.
Xbox Platform CVP Mike Ybarra discussed mouse and keyboard support for Xbox One during a panel at PAX West this week, stating that Microsoft is taking particular care to ensure that developers are smart about when to allow the functionality.
Keyboard and mouse support is definitely coming. We have to be very smart in how we do that. We'll leave it a lot up to developer choice. A lot of people tweet me and say "you can't do this because of fairness," and we understand that. We run two platforms; the Xbox platform, and the Windows platform.
And so, when we bring keyboard and mouse, we'll coach developers and say "look, you've got to think about your multiplayer pools, if you have a competitive game, people are probably going to want the choice to say I'll play with other keyboard and mouse people or I'll play only with controller people, or that I'll play with any of those.
So you'll see our first games supporting keyboard and mouse soon, I can't announce what that is, but soon. And based on developer interest, they'll choose to do keyboard and mouse, or not!"
There is a lot of anxiety about the inclusion of mouse support on Xbox One, primarily from players of competitive shooters. If you have a mouse, you can turn very rapidly without sacrificing aim, whereas on controller, turning up the horizontal joystick speed might make you turn faster, but you'll lose accuracy in the process. Microsoft has already been experimenting with mixed input playlists on Gears of War 4, and if Gears is any indication, the company wants to make sure players have a choice over who they compete against.
Therein lies other problems though. If every mutliplayer game on Xbox is suddenly split between keyboard and mouse vs. controller-only playlists, it could cut player pools into pieces, reducing matchmaking speeds. Microsoft will likely leave it up to developers on whether or not they implement these features, but I believe the addition, over all, is incredibly positive.
Games like Cities: Skylines would have been ported to Xbox One far quicker if the developers didn't have to rework the entire UI for controller support. There's probably a future for mouse and keyboard-only games, such as RTS' like Age of Empires, and maybe MOBAs like DOTA2 and Heroes of the Storm. And this even extends to non-gaming apps, like Office UWP. For students, an Xbox One could become a pretty solid gaming / productivity PC on a budget.
The potential here is truly massive, we'll just have to wait and see whether developers bite or not.