I encourage you to think about the reasons behind this. It is true that some input devices provide a competitive advantage over others, e.g. keyboard/mouse is typically better than a gamepad. However, there is not a 1:1 connection between platforms and input devices. As of late last year, Xbox One players can use a keyboard/mouse with their console (I believe Roblox is looking into adding support for this). Similarly, PC players can use a gamepad. Many industry games are starting to do input based matchmaking for this reason.
So any argument that says “I want to segregate my players based on platform because of a competitive input type advantage” seems like a suboptimal solution. Instead, segregate your players based on input type.