One of the solid habits of From Software is to expand their dark worlds through new content. In their latest titles, DLCs has been a rule to comply that probably From will keep in Elden Ring.
Future Press, publishers of the official guide of Elden Ring, have delayed the Volume II of the Elden Ring guide until early 2023. First volume is already available and the second one was expected for Christmas initially, by we will have to wait for it a bit more. They commented the following to explain the delay:
We’re still hard at work on Volume II, and have made the tough decision to delay its release until early 2023. We’re striving to include all there is to know at the time of publication, making it accurate and useful long after its release.
I would like to remark this excerpt “to include all there is to know at the time of publication”. They could be hinting for new material. Of course, this is not a confirmation, but it points in that way.