I think the epilogue of DH leaves things wide open for JK to do a retrospective / "what happened during the intervening 19 years", after everyone's had a bit of a HP rest (say about 5 years). Certainly the way the whole last few pages of DH was written points pefectly towards that - and maybe then we can get some of the huge gaps filled in!!!
I wanna know what happened to: the Wesleys (how did they cope with Fred's death?); McGonagall, Sprout, Flitwick & Slughorn; most of the students whom we know didn't die, especially Luna, Seamus, Dean & Malfoy; the Dursleys......and of course how Harry's, Ron's and Hermione's careers panned out. And that's just for starters!!!