Not sure what this achieves from Nelson's end. An extra month or two?
Meanwhile Costello hasn't resigned. I don't think we will know the end of this story for at least 12 months, but instability in the party favours him over the long term.
UPDATE: For Nelson, it achieved early retirement from the job as leader. If Malcolm T performs well, that is not just the end of Nelson but certainly farewell for Costello, sooner or later.