I think alot of us assume it was just going to be the Core Books + Vecna, and maybe a setting book, seems like it could be more.
It was hard to say, when they had just announced the four products. Worth remembering that in 2014 they had way fewer resources, and put out 6 major products: 3 Core books, a box set and Teo longer Campaign books.
Based on what Perkins and Crawford have been laying down in their recent video interviews and convention appearances, sure seems like we may see at least 3 if not 4 non-Core products next year. What we now know about next year:
- In addition to the Core, we will see more books next year, plural, and the way Ceawford and Perkins spoke in that latest interview it sounded like more than 2.
- A Vecna villain campaign that involves travelling between multiple worlds as a celebration of 50 years of product: we know that Death House from Cursr of Dtrahd I'd involved, and that Eberron and Dragonlance will also tie in here. This also appears to involve the Rod of Seven Parts as the anti-Vecna MacGuffin
- Something involving the Infinite Staircase, maybe the same product, maybe a different book, maybe both
- Something involving Drelzna from S4 The Lost Caverns of Tsojcanth. Maybe also the Vecna campaign, maybe something else.
- Something to do with the Wolf-in-Sheeps-Clothing from S3 Expedition to the Barrier Peaks. Maybe also the Vecna Campaign, maybe something else
Still not much to go on, but there is good reason to believe we are looking at multiple books. Also, Winninger's aged hibt about a Setting revisit...Forgotten Realms slipcase?