I realize I'm all over the place here, but here is another way to decrease they coin supply temporarily: have the protocol sell bonds. In this way, the protocol can borrow coins from users (reducing the coin supply), then make interest payments, and return the money at maturity. This would be a good way to handle a temporary oversupply of coins, but not a good way to handle a coin supply that needs to keep shrinking (since more coins are ultimately introduced by these bonds through the interest payments).
So people would have an option and mechanism to buy the bonds? I kind of prefer a dynamic demurrage-like factor that just multiplies every coin's value by a number based on the linked commodity price/index. People are already used to seeing their account balance go up and down by small amounts ("interest" and "fees" or perhaps "taxes").