Biblical Criticism & History Forum - earlywritings.com

Taylor notes that the Refutation of All Heresies

developed Irenaeus in two passages (in Ref. 7:33:1–12; 10:21:1–3). [It] too states that Cerinthus thought that the world was made by a Power ‘which is above the all and not knowing the God above all things’ (Ref. 7:33:1), and is ‘angelic’ (Ref. 10:21:1). Jesus was not born of a virgin but from Joseph and Mary, but he was more righteous and wiser than other people, or excelled in ‘justice, prudence and understanding’ (Ref. 10:21:2). After his baptism Christ descended into him in the form of a dove from God, and he proclaimed the unknown Father and performed miracles. In the end, Christ flew away from Jesus. Jesus suffered and rose again but Christ did not: the spiritual Christ departed ‘at the end of the Passion’ (Ref. 10:21:3, cf. 7:33:12).

And that

... The God of the Jews is then defined as the Creator, distinct from a Platonic impassable entity. Here Ps.-Tertullian does not distinguish between the earthly ‘Jesus’ and the heavenly ‘Christ’ in Cerinthus’ theology but he does emphasise Cerinthian belief in Jesus’ humanity from birth. He states that Cerinthus believed it was angels who gave the Law to the Jews, thereby apparently severing ‘the God of the Jews’ from the true God.

I think that was the driving force behind the views of Christians later declared as heretics: some Greek philosophers from the time of Epicurus saw that God was a remote perfect being. And as a remote perfect being it had no needs, no reason to interact with humans. The solution for Jews, Christians and pagans who were struck by this logic had a solution: an intermediary. For pagans it was the Demiurge; for Jews it was the Logos/Torah, the word of God, or angels; finally for orthodox Christians Christ took up that role.

Since Greek philosophy was the 'science' of its day -- so everything had to conform to it -- Cerinthus's views evolved from the proto-Ebionites: Jesus was born normally of Joseph and Mary with the Christ element descending separately due to his perfect adherence to the Higher God. He collected sayings and stories from Paul, the Old Testament and other sources to create proto-gMark.

If Cerinthus did write gMark, then the ending would have included the Christ element ascending separately to Jesus, an ending the later orthodox group would have resisted. (NOTE: It doesn't have to be Cerinthus, just any Greek-educated pagan Christian trying to reconcile Jewish Christianity with the science of his day.)

I can't prove any of it, but it really all makes sense, to me at least! This goes straight into my head canon.