There is/was a lawsuit challenging the multiple reporting requirement imposed by DHS. I'm sorry, but I don't know the outcome.
For what it's worth, regardless of the outcome of the suit, there is still a reporting requirement when multiple handguns are purchased from the same dealer in a short timeframe. That requirement has been in place for many years and applies across the board--not just in the 4 states mention. I don't believe it would be affected by the outcome of the suit.