I’m over in Wisconsin nowadays. Paul might appreciate knowing that where I’m at, it’s 30 degrees (Fahrenheit) colder than Helsinki today. The lakes all froze over last week. But in California there was an earthquake this morning, centered under my old apartment, which I missed.
The absence of the entire verse would also explain the patristic evidence. It might even explain it better. Here is Origen on 5:1 (mentioned by Hort):
Ἐὰν δὲ αὕτη ἡ ἑορτὴ <ἡ> τοῦ πάσχα ᾖ—οὐ <γὰρ> πρόσκειται τὸ ὄνομα αὐτῆς—, στενοχωρεῖται τὸ ἀκόλουθον τῆς ἱστορίας, καὶ μάλιστα ἐπεὶ μετ’ ὀλίγα ἐπιφέρεται ὅτι «Ἦν ἐγγὺς ἡ ἑορτὴ τῶν Ἰουδαίων, ἡ σκηνοπηγία.»
So Origen passes over 6:4 completely, looking ahead to 7:2.
Just looking at the text, I would say that 6:4 is less motivated by the surrounding text than 5:1 or 7:2. It is very similar to 7:2.
As an interpolation, ἦν δὲ ἐγγὺς ἡ ἑορτὴ τῶν Ἰουδαίων makes sense. A scribe adding it as a marginal note might be saying: “John 7:2 explains the crowds.” Though in my opinion, the festival of booths is not a very good explanation for crowds on a mountain. Still, I can imagine someone thinking that it was.
I don’t see how the full ἦν δὲ ἐγγὺς τὸ πάσχα, ἡ ἑορτὴ τῶν Ἰουδαίων could be an independent interpolation all at once. It makes far less sense as a marginal note. So if 6:4 was originally not present, I think there would have to be a two step process, with ἦν δὲ ἐγγὺς ἡ ἑορτὴ τῶν Ἰουδαίων coming in first, and then τὸ πάσχα.
On the other hand, I don’t see any way to say that ἦν δὲ ἐγγὺς ἡ ἑορτὴ τῶν Ἰουδαίων couldn’t have been John himself. The manuscript evidence against it seems late, and perhaps the verse dropped out as a mechanical mistake? I imagine that someone would have to know more about the characteristics of 472 and 1634 (and whatever others are meant by “pc”) to make a determination.