An important part of the Xbox One's mouse and keyboard support is now in place for some players -- namely, the mouse part. Members of the Alpha Skip Ahead and Beta programs can try mouse support through a Quest in the Xbox Insider Hub. You'll be limited to Warframe, but this gives you a chance to see how the full mouse-plus-keyboard combo works in practice ahead of the finished release.
The feature doesn't require any specific hardware. Like before, Microsoft is also promising optional, game-by-game compatibility rather than universal support. It's trying to walk a fine line where it offers advanced control for some games without providing an unfair advantage in competitive multiplayer scenarios. You probably won't play some of the hottest online shooters with a mouse and keyboard, but you might have a much easier time in cooperative games and solo titles.