One thing you wrote, Christopher, did catch my eye and I was wondering what you meant:
And by the same token, it's too early to say it's the end of that arc, since we don't know yet whether Brinkmanship will be a separate thing or a direct continuation of the same threads, and we don't know whether future works will do a similar kind of retroactive arc creation/consolidation.
What threads do you feel require continuation or are left "hanging" post-RtD?
I didn't say I felt anything of the sort. But I'm not the one writing the next book. If PoN/RtD could take previously standalone books and unify them into a tighter narrative, then another author could take a seemingly "finished" story and decide to carry it further. I'm just saying that the way the storyline looks to you now isn't necessarily how it might look a year from now after more has been done with it -- just as the way it looks now isn't the way it looked a year ago.