Though I have not played 3rd, from what I've understood from some of the tidbits I've read about it & the way people comment on its importance & connectedness to pretty much everything, isn't the best way to describe it that it acts as a kind of bridge between Trails in the Sky FC + SC and pretty much everything that comes afterwards, rather than being "just" an epilogue? So while it expands on some stuff that's already talked about in the first two games, it also introduces quite a lot of completely new plot threads that will be more or less important in both the Zero + Blue duology as well as the Cold Steel trilogy. I mean, epilogues can and often do set up future storylines in fiction, but isn't 3rd kind of too far removed from FC & SC (i.e. focuses on different main characters, whole new setting) & the new story stuff a bit too significant that calling it an epilogue doesn't quite do it justice? To me it sounds like rather than Trails in the Sky 3rd, the game should've been called something like Trails to the Future with just how much it is seemingly focused on setting up subsequent games.
That's just the impression I've gotten without having played the game, though, so maybe I'm not one to listen on this subject.
It sets up a lot of plotlines that are explored in the later games, but it isn`t that removed from the FC+SC duology.
From what I played, it acts as a epilogue to a lot of characters, explaining what happened to them after SC.It also goes deeper on the relationships and influence of a lot of secondary characters too, people that were important in the duology, but didn`t had their proper time in the spotlight.You get to know more about Mueller, Kilika, Rin, for example, and they influence future games in some considerable ways.
I think it`s too bad that people only recently took notice of this series and now there`s this big elephant in the room about what to do regarding The 3rd and Zero/Ao. If XSEED does not localize, I guess the better solution will be making a traslated walkthrough like what RGG Subs does with Yakuza games or what BlackRaen has done with Ciel nosurge.