In a scenario where the Rashidis defeated the Saudis during the
Saudi-Rashidi War, rendering the House of Saud a historical footnote and unites Arabia in a manner akin to the Saudis IOTL, how does Arabia develop? What does a Jabal Shammar which encompasses the territory of OTL Saudi Arabia look like? How does the lack of Wahhabism affect the wider Middle East?
Without the Saudis, the British probably don't have split loyalties and so the Hashemites end up in charge of Nejd and Hedjaz instead of ibn Saud kicking them out. Those states might remain independent.
Anway, we're looking at presumably a strong ally to the British, but also to Jordan and Iraq. It would be interesting to see if this kingdom is as willing to play ball with the Americans over oil, or if it will stick to the British, or play the US and UK off of each other. Plus, likely to modernize, etc.
One thing that's interesting is whether this kingdom/these kingdoms might fall to Arab nationalist republics, where the Saudis did not. Unfortunately, I don't know enough about Arab nationalism in Arabia to say more.