True. It was every Muslim scholars (except Khawarij, some Shiite sects and Salafi) to preserve the Ummah and avoid Fitna (discord). The difficulty I see here is to create a Ummah that would take Mu'tazalites as a mainstream ideology with Greek influences (perhaps Gnostics?) that are not immediately labelled as Bidaa (innovation in religion). Can you even imagine the fierceness of a Greek Khawarij movement after the Arabs shun Greek culture or a Khawarij revolt against the nobility of the Mu'tazalites. Like I said earlier, I feel Greece could become like Iran, Muslim but opposed to the widespread use of Arabic and somewhat different in theology an application of Shariah, perhaps icons are slightly more accepted.
Interesting ideas. Kawarij ideals IOTL seem to work better in lightly urbanized milieus, so I think that the opposition in Hellenic areas is more likely to embrace an analog to Zaydi Shi'a, but I think you are spot on.
Answering the Syriac connection, I was not saying built off of as in the language itself but it is obvious that Kufic and Naskh were built from the Syriac script as used in Iraq abd Edessa from 200 BC till the 500s AD.
Actually the overwhelming consensus nowadays is that the Arabic script evolved from Nabatean script, not Syriac (as posited, among others, by Starcky in the sixties). Recent findings in Saudi Arabia appear to confirm this strongly, although they are not published yet. However, there is an undeniable Syriac influence in some letter shapes, particularly in Kufic. When I studied Semitic Philology some years ago, Syriac derivation was still considered a serious hypothesis by some, but the work by Gruendler and Healey in the nineties is fairly compelling about the Nabatean origin of Arabic script, and some later discoveries have tended to confirm it. (There is a Saudi scholar who suggests a South Arabian derivation. His ideas are interesting, but, as far as I can tell, pretty weakly supported by any known evidence.)