The icing boots were extended shortly after the accident and the plane can take icing conditions.

It was not all design flaw that brought that flight down. Holding below minimum recommended icing holding speed did not help matters any. It was your usual "series of events" that ultimately led to the crash.

The planes were sent south, but they are back in DFW now, where there is significant icing possibilities. And many operators continued to fly the ATR in extreme northern climates. I think the transfer south was part for public perception and part to make way for RJs.