What if the Elagabal cult is successfully implemented as a state religion in the Roman Empire ?
Emesa would have a lot to gain.
I second the idea that Elagabalus would have to be more discreet in his proclivity toward his namesake deity and be a lot less morally depraved. The religion had some popular support, statues of the deity were apparently found as far away as the Netherlands, and Aurelian thought the deity played a role in his defeat of Zenobia.
The best chance for it to become a state religion is to have Elgabalus's decrees raise its standing enough so that it becomes even more conflated with Sol Invictus, and becomes the basis for the increasing amount of Sun worship among the military. That, coupled with more Severan emperors who came from Emesa, could result in a Sol Invictus/Elgabalus cult becoming the State religion after enough time. However, just like Sol Invictus worship, it would be mostly focused on men in the military and the lower classes and women might still become Christian, creating dueling monotheistic religions.
The first long term geopolitical consequence I can think of is that perhaps relationships with the Zoroastrian Sassanids are better, as the Sassanids worship Ahura Mazda, god of fire, and Elgabalus is a Solar deity, thus relatively similar.