birddog,
Theoretically, any control system you can imagine is possible. However, once you get into certifying the FBW system you will find some restriction. Imagine looking at a helicopter cockpit and you see one joystick, nothing else for 4-axis flight control.
In my opinion, this will be a challenge in the future. We can build something that is easy to fly and seems intuitive, but may not meet certification criteria. Not an insurmountable obstacle, but another challenge (=expense) that may delay commercial FBW.
Cheers,
Matthew.