M/KB Support?

Yes! KB&M support will be a thing on Xbox but currently there is no release date. I think the only game that support KB&M right now is Minecraft

Huh? Maybe you should re-read the Terms of Use. Only authorized accessories are to be used with the 360 for gameplay. There are no authorized accessories to provide KB/M support. By definition, there is no legitimate method available to support KB/M on the
360 for gameplay.

The capability is here, but it is not widely supported. I heard that Minecraft for Xbox One fully supports this kind of input at the very least.

KB+M support solely depends on the game developer. The main hindrance to this entire thing (in general) is the controversy over the fact that KB+M users have the advantage of accuracy over controller users, throwing out balance and making multiplayer games
unfair.

In the case of Fortnite, you'll have to get in touch with the developers (Epic Games) to see if they are interested in implementing KB+M support in their game. Microsoft is not going to force KB+M input over all titles anytime soon, as far as I can tell.

It will be up to the game devs to decide if they want KB&M support in their games on the console. It's possible that some FPS could have separate lobbies for KB&M users. That would be my preference at least.

I do not believe there a single Title with Mouse and Keyboard support that puts M&KB against Controller. To my knowledge they all have a lobby system set up that puts you in games with controllers players or M&KB players. Some would also argue that controller
has an advantage over M&KB, to each their own.