The ideas of what kind of magical foci might come up with for Peace Talks or down the line is a worthy discussion, but I really hope the basic thing Harry is forced to do in Peace Talks is be a detective again. Aside from political maneuvering and fighting people and things that want to take him out, I'm hoping something happens that creates mystery and Harry has to sleuth it out, or else.
I don't think we've had a good mystery for Harry to unravel since Turn Coat. Changes had some detective work in it, but the focus of the story was Harry putting a team together to go kick some Red Court vampire ass and get his daughter back. In Ghost Story Harry didn't really solve the mystery of how he died, he sort of backed into the answer. In Cold Days there was the mystery of why Mab wanted Harry to kill Maeve, but it was secondary to Harry keeping Demonreach from going boom. Also, for me, and I bet for most other readers, why Mab wanted Harry to kill Maeve was less important than seeing Harry reconnect with friends and family. Finally, in Skin Game there were the mysteries of what Nicodemus wanted and how Nicodemus would try to double-cross Harry, but in the end we found out Harry had his own ringer in Nic's crew, so Harry didn't have to solve anything, he had his own countermeasure already in place. I think the Dresden Files as a whole needs a good mystery to revitalize it; to get the main character doing the thing he does best, and reenergize the fans too.