This thread isn't entirely serious; given the extreme outlandishness of the scenario, I thought that would be obvious. For these purposes a "Caliphate" just means a united state with Islam as a nominal ideology, but not one by any means more extreme or violent than the Arab people would want to live under, or one too violent to coexist in the international community. A Caliph is a person with ultimate religious authority and a certain amount, but probably not absolute political power.
But I think there would be some advantages of "pan-Arabism", (as well as other transnational movements, such as the E.U.), and I've also come to accept that Western-style social liberal secularism is not the only legitimate path for people in the region to follow. When given the vote, at the very least, nominally Islamist parties such as AKP win (and this in a country considered more moderate than the Arab countries). Mainly I made the thread to make the points that I made: the plethora of wars and failed states in the region would be lesser if there was a strong single state. It is a shame that oil wealth is concentrated in reactionary, unpopulated desert monarchies. Large entities (The U.S., the E.U., the BRICS) tend to have a lot of clout whereas a divided people (such as the Arabs) tend to be victims. And so on.
There are some good arguments for Pan-Arabism, but the idea of an Caliphat would be the solution seem quite counter-productive as such a state would build on Islam and not Arab nationhood.