Polytheisms (or 'monocultisms', i.e. worshiping almost exclusively a deity, or a divine couple, in a polytheistic background) are in great difficulty facing 'conquering' monotheisms such as Christianity and Islam. Because 'paganism' is more tolerant (the monotheistic Persians did not forcefully convert conquered peoples to Zoroastrianism) and thus in a sheep / wolf position.
What type of 'revived pagan' cult Julian could have promoted. Isis? Mithra?
It could be of interest that, while theologians were excommunicating (and persecuting) each other about the Trinity, popular faith was tending to install a biological triad (the Father, the Mother, the Son) with similarities with the familial trio Osiris, Isis, Horus. And the cult of Saints was evolving to an unconfessed form of 'soft' polytheism?