I don't think it will work. Because bitCNY is a derivative asset and not actual CNY, the market can always adjust its demand to appreciate/depreciate bitCNY. For example, if we consider an extreme example, make feed price = 2x market price on Bitshares, internal price is 0.65, feed is now 1.3, so now margin calls can only go to (1.3 - 0.13), it doesn't mean the market will suddenly buy up all BTS from 0.65 to the margin call price.
I guess the effect it will have is margin calls won't be eaten though
Maybe it will also affect settlement operations by devaluing bitCNY in a bear market. If that is the case, maybe it can work. But as I just said, because bitCNY is a derivative the market can just increase demand for bitCNY when it is devalued