Saru implies to Burnham that she should consider making Book the new first officer on Discovery. Book is not a part of Starfleet or any other similar hierarchical organization. Presumably Saru makes the suggestion so that his own choice of ensign Tilly as his first officer in “Unification III” is no longer the wildest choice of in the history of Starfleet.
On rewatch, I wonder if he was on the way to suggesting someone like Book when he was interrupted. But then again, he's known for his, uh, original thinking when it comes to XOs, as you noted.
”Diary’s Romulan; Federation’s got no claim to it.” it was established in “Unification III” that the Romulans had reunified with the Vulcans at some point during the in the past, and in “All Is Possible” Ni’Var rejoined the Federation.
Ni'Var may or may not be considered the legal successor to the Romulan Free State, which in turn may or may not be considered the legal successor to the Romulan Star Empire. I think "ownership" of these ancient artifacts could be very murky indeed. And no one even mentioned how salvage rights work in the 32nd Century.
Quick, get Alex Kurtzman on the phone so I can pitch Star Trek: Space Maritime Law.
On rewatch, I wonder if he was on the way to suggesting someone like Book when he was interrupted
Agree with this, it seemed like he was using Book for context, not for a real suggestion. Saru respects what Booker has done for everyone, but I don't think he's a real big fan of the guy, and certainly doesn't think he should be the XO of a Federation ship.