I may add that it would be nice to know if a joystick is an xbox 360 controller or not.
On windows people could use xinput for such cotrollers, in parallel with sfml for the other normal joysticks. So there should be a way to avoid allocating the same device to two different players.
Now I use xinput and directinput at once and there's an official (bad looking) piece of code for directinput joysticks to tell if they are 360 controllers. If so I skip those and open them through xinput.
I suppose this could usually work by searching 360 in the name of the driver/joystick, if nothing better is available.
I think other libraries/drivers are available officially or not for wii and sony controllers. And with the new magic wands and other crazy stuff, it would be cool to have some extra support for such joysticks, or at least a way to support them in parallel through other libs.