The uptick rule will not have any real impact on a typical trading day, only on high volatility days. Even then the impact will be minimal. Also reinstating the uptick rule will not have any impact on the existing shorts so there is no reason for the 12ml short shares to start heading for the door at the same time. The only impact it could have is to slow them down when they try to re-short in the future.

If they tightened the enforcement of naked shorting, now that could cause a hasty exit by the shorts.