While Microsoft hasn’t announced any official support for keyboard and mouse on Xbox One just yet, it also doesn't look like it has any plans to stop those wishing to use such a setup.
Despite the fact that some players have raised concern that keyboard-and-mouse users could have some advantage over those using console controllers – particularly when it comes to multiplayer shooters – Microsoft has said it has good reasons for not stopping them.
According the Xbox engineering lead, Mike Ybarra, Microsoft actually could block keyboard and mouse setups on Xbox consoles but actively chooses not to.
The first of these reasons is that Microsoft would rather not place limitations on developers and the games they’re creating. The second is that having the option of keyboard and mouse support can be helpful from an accessibility perspective.
We could but there are helpful scenarios with these devices (accessibility for one). Our general approach is to empower the developer to manage their game how they want.February 18, 2018
Besides the empowerment for users and developers that keyboard and mouse support brings, it’s unlikely that Microsoft would want to block it given it’s already said that it has plans to introduce official support.
We’ve been hearing talk of official mouse and keyboard support from Microsoft for around three years now but it’s yet to materialize. As recently as September 2017, Ybarra said there are definitely still plans to make it happen but there still wasn’t any word on when.
Ybarra acknowledged the concerns that there may be advantages and disadvantages to players but said that Microsoft will 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 Windows platform and the Xbox platform.“
Developers have the choice to use APIs that detect and not allow these. It’s up to them, but the capability is there. https://t.co/jE97R6oj0cFebruary 18, 2018
One solution which retains choice for players and game creators is that developers will create systems within their own games which will allow players to decide if they’d like to play against those with different setups from themselves. In Gears of War 4 for example, there’s cross-play support between Xbox and PC, but console players are able to choose whether or not they’d like to play with PC users.