Problem is that Hellenism was along dead religion and Christianity and Islam were much stronger than Hellenism ever was. Christianity already gave ruler an ultimate mandate to rule all people in name of God so Hellenism can not give more power to ruler. Some historical parallel of revieve old religion could be taken from China, first revieve of Confucianism and second revieve of Taoism during Tang dynasty. Revieve of Hellenism would be a nice end game task, after most of Rome is beign united.
So what kind of religion would Hellenism be? First you should reform it but it should be very easy with a huge empire. Only one Hellenistic religion would be really boring so I suggest three different path: Neo-Hellenism (Concubinage, sex-equility, holy wars) Old-Hellenism (divine blood, excommunication, can hold temples, free divorce) and Classic-Hellenism (can hold temples, free divorce, excommunication, polygamy). There would be no heresies of Hellenism but maybe low religious authority should spawn Christianity.