The every-other-line-is-180 degrees thing could be explained by two people (such as a parent and child, a couple, or two chiefs or priests) sitting facing one another and working on the workpiece together. It could therefore have ritual semantics rather than merely literary. A test might be to look for alternative micro-stylistic signatures on alternate lines which could suggest dual authors.
The quote "According to oral tradition, knowledge of rongorongo was restricted to a class of priests known as tangata rongorongo" might support this thesis.
LibGen's latest paper on the subject dates from 2020 and summarizes: "among the many published proposals, the only one for which there is more than a modicum of scholarly agreement is the 'Lunar Calendar' on tablet 'Mamari' (Barthel 1958; cf. Guy 1990)."
> These are arranged in horizontal lines, but every other line is written upside-down, a style known as reverse boustrophedon. This means that anyone reading the texts would have had to turn them through 180 degrees at the end of each line.
I thought that "turning 180° at the end of each line" was not the most likely explanation, but rather that it was meant to be read by two people standing face to face, in a kind of dialogue or maybe echo/repetition. If that's correct it would be a stage script or used of some kind of ritual. (But it doesn't need to have different authors or scriptors; the same writer could carve each line one after the other.)