Recently appeared is Darrell Hannah, “The Vorlage of the Ethiopic version of the Epistula apostolorum: Greek or Arabic?” in Meron T. Gebreananaye et al. (ed.), Beyond Canon: early Christianity and the Ethiopic textual tradition (London: London: T&T Clark, 2021), 97–116. Fr Darrell is nearly a neighbour, so giving this a puff is a particular pleasure.
The church order connection (I always try to find one) is in his reflection on the apocalypse of Testamentum Domini. The relationship between this apocalypse and that preceding the Epistula in the Ethiopic witness (the Discourse in Galilee). The relationship between these two apocalypses has long been an interest to me, so it is a boon to see the evidence laid out so clearly. Fr Darrell actually suggests that the Epistula itself may have been a source on which the apocalypse of the Testamentum drew. This would make sense given the recent ascription of all this material to an Asian provenance.
Although nowhere near as accomplished as Fr Darrell in examining this material, I have for a long time taken a punt on the Ethiopic being a direct translation of the Greek. In particular I had in mind the passage where Jesus speaks of the Pascha which the disciple who is released from prison will keep: he refers to “that which is in my remembrance and my agape” (in the Coptic) or “my agape and my memorial” (Ethiopic). The Coptic translator seems to assume that the “memorial” is the Eucharist. To me it seems more probable that a distinct rite is intended, and that the Ethiopic translator has correctly rendered the Greek (which may well be μνημόσυνον.) The statement of an expert on this material that the Ethiopic is taken directly from Greek, and not via Arabic, renews my confidence.