Arab nationalism wank--the House of Sa'ud is overthrown by one of the Arab nationalist/Arab socialist movements in the country, who proceed to form a union with North Yemen and "export the revolution" so the speak to the other states of the Arab peninsula. Even if it's only a loose federation or ephemeral like the United Arab Republic, they might be able to form a union with the other countries of the Arab peninsula. Not sure how plausible Iraq, Syria, Jordan, or Palestine might be, especially long-term.