This is the scenario as I see it. Kevin Rudd wants revenge on Prime Minister Gillard. She deposed him and he naturally is miffed about it. He probably heard that Gillard is planning to sack him from his job as Foreign Minister. Therefore he pulled the rug from under her feet, announced his resignation just before evening news time in Australia and now will see how things pan out. If he gets support for his challenge, if a challenge is called, he most likely will not go along with it.
He will bring the Labor Government down. This will be his revenge on Gillard and the party. He will probably do this by the Ides of March, an auspicious day in History. Then he will head overseas and take up the job he was seeking. U.N? Who knows?