I appreciate the breakdown, SinisterSamurai! It's weird that the tau would swear the rescue mission to secrecy, especially if 1) the tau are also
aware that aun serve on the front lines (as your culture bulletpoint says), and 2) the mission were successful. Surely the tau are aware that sometimes ethereals perish violently, and that daring rescues are the stuff that legends (and propaganda films!) are made of. Just look at how Aun'vre came to prominence.
Beyond that, I'm glad the ol' u'it
show back up. I don't know precisely where it's been used before -- probably Fire Warrior
? -- but our lexicon has it defined as "a species of cub-raising animal on T'au." It's always nice to see writers remember and incorporate older stuff.
Any explanation on why a 'ui was in charge of the overall mission, despite being outranked by his erstwhile subordinates? (Not that this bothers me. The tau not sticking to hierarchy and graciously stepping aside when they realize that a subordinate is better equipped to lead in a given situation is very not-human, and I approve. Assuming that's what happened here.)
Finally -- and based on how I Am Slaughter
introduced some ideas just coming to fruition in The Gathering Storm
("Lord Guilliman" as a position on the High Lords, for instance) I wouldn't be surprised if Prefectia is the flashpoint for our coming "End Times" story. Smells like Necrons.