Motivating someone to move on to find a better place for themselves is something that must be built into the core of the new organizational structure. Ideally it happens organically, so it becomes obvious to the person that it's time to seek better experiences. It would be especially great if it was a celebration -- celebrating the enlightenment and awareness that this person achieved to reach the point where they knew they wanted to move on.
Fractal Profit Sharing will stimulate people to find what they're good at -- better ways to create and serve. A person will discover a way to better serve everyone rather than just sliding downward within a job. The concept of "job" will not be as restrictive as it tends to be now -- when a person comes in, they know that their "job" is to find the way they can best serve the company.
To solve this problem we must move away from defining a job and then finding someone who fits it (the "putting pegs into holes" model). We start by knowing that everyone is different, and each person's optimal productivity and happiness will be produced in different ways.
I know this is hard to imagine within our current structures. My "job" is not only to think outside the box, but to imagine a world without boxes.