Personally I'd like to see something with the painted world, but I don't feel like that will happen. Fromsoft has a habit of setting there dlc's as if they were from an earlier time: Artorious of the Abyss and Old Iron king dlc's are really easy to see this in. If I had to take an educated guess I have 3 theories. 1. New Londo and the ways in which the abyss was creeping to the surface. 2. Irythil when pontif began his take over. However I see this less likely as we don't have details on other knights that served him other then Vordt and Dancer. 3. The fall of Lothric Castel. It happened, but we didn't see it. This could have some really cool set pieces and insight into ocierous and the heavenly daughter.