WI/AHC : Hashemite controlled Arabia

As the title says, what if the House of Hashim controlled all or most of the Arabian Peninsula?
a) What PODs could achieve this? (To my knowledge they used to control Hejaz till 1925 and Iraq till 1958 and very briefly Syria. They still are in power in Jordan which perhaps the most stable country in the region.)
b) how would a united Arab kingdom look like with Hashemites in power and all of their territories united into one kingdom i.e. how would they do economically and militarily? What would the social conditions look like?
Bonus points if they can legitimately claim (and hold) the title of Caliph.
 
There were already some AHC's that tackled such scenario; most of which suggested that if the British Government seriously considered the offer/proposal of the India Office.
 
What 'indian proposal'? And I thought it was okay to have a discussion on this even if there were threads before. I'm new here so I don't know all the rules.
 
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