I would love to help out, but I have limited knowledge of what force-feedback controllers are capable of.
My main concern is to establish relative positions of rumbler type controls. So we can rumble left or right hand for instance. And perhaps establish an axis and properties so that the sign of magnitude of the force has meaning.
E.g. a steering wheel with force feedback needs to show up as something with a rotational force feedback where +1 forces clockwise and -1 forces counter-clockwise.
A joystick with force feedback (other than a rumbler) needs to establish a force for X & Y axis in a similar way.
A flight yoke might have both properties rotational and directional forces.
If you build these basic concepts into the FF APIs I think they can be made to fit an arbitrary controller. Likely many that don't actually exist
, but why not future-proof things a tad if it doesn't get in the way.