Well the way I see it is this:
Let's say my 40% balloon after 4 years is 35k. I walk into the original dealership to trade it in for another BMW when the current lease is up. I would imagine they would have access to the amount of my balloon before they tell me how much the car is worth - so what is the incentive for them to say my car is actually worth 38k so here is another 3k towards your new car? If the car is worth less then it is just a BMW Finance problem.
Maybe I am just being overly cynical.
Another thing about full circle - I have got 60,000km over 4 years. I am allowed an extra 5,000km, but at a cost of 75 cents per km. Over that and full circle thing is nullified.