The idea is probably, like 2010, to help the eventual Republican candidate by damaging Democratic candidates. So far, only Sen. Gene Jeffress has announced as a Democrat, but further developments are expected. However, the crossover Republicans who helped put Morrison in double figures in the 2010 primary won't have a free shot in 2012. They'll have to forsake a vote in the contested Republican congressional primary.
PS — Morrison told AP he plans to move to the 4th District. But district residency isn't required for congressional candidates.