Does the question of the historicity of the gospel come down to a question of whether the text originally intended to portray an earthly or heavenly stranger? If we acknowledge Joseph was a very late addition then a mother specifically named 'Mary' was yet another layer of the same onion. While Luke 8:19 - 20 reads:
Now Jesus’ mother and brothers came to see him, but they were not able to get near him because of the crowd. Someone told him, “Your mother and brothers are standing outside, wanting to see you.” He replied, “My mother and brothers are those who hear God’s word and put it into practice.”
The Marcionite version clearly resembled what appears in our canonical Mark for it adds 'Who is my mother and my brethren?', not recorded by Luke, but present in Matt. 12: 48 and Mark 3: 33. Notice also that there is no specific mention of a name for Jesus's alleged 'mother.' The purpose of the narrative was to reinforce that 'everyone knew' that Jesus claimed to be from heaven after his appearance in the synagogue.
From Epiphanius, Panarion 30.14, writing of the Ebionites:
Παλιν δε αρνουνται ειναι αυτον ανθρωπον, δηθεν απο του λογου ου ειρηκεν ο σωτηρ εν τω αναγγεληναι αυτω οτι, Ιδου, η μητηρ σου και οι αδελφοι σου εξω εστηκασιν, οτι, Τις μου εστι μητηρ και αδελφοι; και εκτεινας την χειρα επι τους μαθητας εφη· Ουτοι εισιν οι αδελφοι μου και η μητηρ και αδελφαι, οι ποιουντες τα θεληματα του πατρος μου.
But again they deny that he was a man, apparently from the word which the savior spoke when it was announced to him: Behold, your mother and your brothers are standing outside, that is: Who is my mother and brothers? And he stretched out his hand over the disciples and said: These who my brothers and mother and sisters, those who are doing the wishes of my father.
From Epiphanius, Panarion 30.16, writing of the Ebionites (de Santos 6; Lagrange 5):
Ου φασκουσι δε εκ θεου πατρος αυτον γεγεννησθαι, αλλα εκτισθαι, ως ενα των αρχαγγελων, μειζονα δε αυτων οντα, αυτον δε κυριευειν και αγγελων και παντων υπο του παντοκρατορος πεποιημενων, και ελθοντα και υφηγησαμενον, ως το παρ αυτοις κατα Εβραιους ευαγγελιον καλουμενον περιεχει, οτι Ηλθον καταλυσαι τας θυσιας, και εαν μη παυσησθε του θυειν, ου παυσεται αφ υμων η οργη.
And they say that he was not engendered from God the father, but created, as one of the archangels, but being greater than they are, and that he is Lord both of angels and of all things made by the creator of all, and that he came also to declare, as the gospel among them called according to the Hebrews has: I came to abolish the sacrifices, and, if you do not cease to sacrifice, the wrath will not cease from you.
From Epiphanius, Panarion 30.22, writings of the Ebionites (de Santos 7; Lagrange 6):
Αυτοι δε αφανισαντες αφ εαυτων την της αληθειας ακολουθιαν ηλλαξαν το ρητον, οπερ εστι πασι φανερον εκ των συνεζευγμενων λεξεων, και εποιησαν τους μαθητας μεν λεγοντας· Που θελεις ετοιμασωμεν σοι το πασχα φαγειν; και αυτον δηθεν λεγοντα· Μη επιθυμια επεθυμησα κρεας τουτο το πασχα φαγειν μεθ υμων;
And they themselves, having removed from themselves the following of the truth, changed the word, which is apparent to all from the words in context, and made the disciples to say: Where do you wish us to prepare the Passover for you to eat? And they made him to clearly say: It is not with desire that I have desired to eat meat, this Passover, with you, is it?
Why don't we just simplify the 'mythicist' or 'historicist' debate into a much simpler question as to whether the gospel originally said that Jesus was an earthly or heavenly stranger? Can there be any objections here?