As of March 28nd, 2019, the current draft of the novel is up to chapter 52. Progress!
Peace Talks may end up being the longest Dresden Files to date, at least in the number of chapters. Cold Days had 53 chapters and the highest word count. Now look at the various issues PT may cover. Obviously something is going to happen at the talks Harry will have to deal with. We haven't seen anyone from the White Council since Changes, so there's bound to be some drama with the Council beyond Harry providing security for White Council negotiators. In Cold Days, Thomas told Harry that Lara was getting scary. As we can expect the White Court to be a part of the Peace Talks I expect we will get some White Court drama too. Marcone should also play a role here. Then there's what's going on with
Justine having Thomas' baby.
Ivy might be called in to help negotiate a settlement, so we may see both her and Kincade. Plus, isn't she a teenager now? That alone could provide some interesting complications. After Molly showed up in the Christmas eve short, short story; I think it's a good guess she may represent the Winter Court in some fashion in Peace Talks. Murphy might be doing rehab after all the injuries she suffered in Skin Game, but she might have a scene or two with Harry. Plus, there's the whole "Murphy's funeral" thing Jim trolled us with.
Now some of the above guesses may not play out, but I bet most of them do. Plus there are the wild cards to consider. What complications could Mavra, Cowl or Elaine bring to the story? Finally, I know some people have thought the Eebs could show up as the leaders of the new Red Court. I'm not betting on that one, but you never know.
So I'm going to make another guess, just for fun. Peace Talks will end up having 55 total chapters, give or take one chapter. I think it's fair to say Jim is getting pretty close to the end.