This is interesting and deals with a real felt problem with tp. While tp does have an array of causative constructions, from making transitive verbs from nouns and adjectives to using 'kama' as a transitive verb (though that has problems), it does not have passives. And they would often be useful. I don't quite see, however, how Tepan's ideas work toward this. 'ijo moku' has perfectly good (though rare) meanings in tp, either "something eating" or "something edible" ("context etc. "). Adding a new meaning hardly seems helpful.
Things like 'ijo moku' are also not obviously (at least) the source of the move from a transitive verb to the genus of its direct object, which seems a simple move in its own right that covers all transitive verbs and prepositions.
Nor does the situation with 'pana sona', which is just incorporation, provide any useful information that I can see.
So barring quite a bit more detail, I don't see a case for passives here.