In case HKD is un-pegged, one should expect huge capital inflow into HK on the expection that value of HKD to appreciate to CNY/HKD = 1.0:1.0 over time. Consider the customer deposits in HK have ~50% are actually denominated in foreign currencies. Consider most of these foreign currencies investments of HK people are all switching back into HK, we will have a situation where there are so much HKD liquidity with too little HKD assets.
So the likely impacts on HK property market may be a lot more 'interesting' that one would expect.