The last point is a misunderstanding of market economics. If take is permanently taken off the market there is an effective reduction in supply. It is definitely not equal to a savings for the reason that you outline: it is permanent.
Demand will stay constant. This will drive up the price, simple supply & demand.
This scheme is game-able if you are allowed to make large sells via the DAIhard platform.
Do not allow sellers to place cumulative sell that exceed .05% of total DAI supply at any time. Or some other threshold based on calculations. Happy to chat about this with you offline.