Anyway, there are a few ways I'm thinking of. They're all things I plan to write; it's just a question of which works best with NP, as opposed to just an entry in Stops on the Way.... (All of them are a little odd, since the story is over, but Tolkien had a hundred pages of appendices after RotK, so...)
The paths I'm thinking are:
Peeta: Tell the story of his time in the Capitol while Katniss is catatonic in Twelve, and Haymitch is drunk. It would involve his apartment, his education, Aurelian and Justinian, and how he chose to come back. Pros: Obviously, it takes place in the timeframe of the story, and it would parallel the Aurelian story that I used as an appendix on Golden Mean. Cons: It's definitely not a story anyone has ever said, "You know what I want to know? How did Peeta live in the Capitol for a few months?"
Gia: The big asked-for -- Haymitch finding out that Gia is Carolyn Odair. I'd expand on the existing story from the request sets, where he goes to Four and they talk at the pier. Pros: People like it, and it would answer a hanging question. Cons: The question isn't hanging that much in the actual structure of the Narrow Path stories, and there's no way to not make it awkward for people who are only reading that particular story.
Indigo: A story of Haymitch's family in the Capitol, as his daughter is exposed to the fame she was born into. Pros: It's definitely of a piece with the epilogue, and it would be a chance to show Haymitch as a dad. I know Indigo better than I've had a chance to write her. Cons: A new character focus story in an appendix? Might well scream (or at least whisper) Mary Sue.
Essay: On the early history of the Catastrophes, and the founding of Panem. Pros: Would be an appendix for a reason -- it's not really story, but might be interesting; the actual sort of thing that should be an appendix. Cons: It basically consists of figuring out how to kill and destroy most of the world, which is a pretty morbid topic.
So, no promises to go by a poll, but I'm interested to see what interests people.
So, which sounds like the best fit for Narrow Path?