Most likely the Saudis are hoping to break the rebel alliance between Saleh and the Houthis, which has been fraying this year. The Saudi war effort is costly and contributing to the flatlining of the Saudi economy. It is unpopular in the West. The battlefield is a brutal stalemate that has produced the worst humanitarian catastrophe in the world. If the rebels split, perhaps the Saudis and their partners can prevail against the Houthis.