I believe the contract states that Disney may suspend the ability to bank and/or borrow. there was speculation that the only time this might actually happen is when it gets closer to 2042. in those last 2 years as members try to use their points.
If borrowing and banking get way out of balance, I'm sure DVC will suspend one or both. As tigger2esq posted, the contracts we signed do make provisions for it.
So the "point borrowers" should thank and encourage the "point bankers" and vice versa. Can't have one without the other!