I expect to see the following books in the next year or two, but in no particular order.
1. Remake of old Adventures compendium: Greyhawk, Planes, or based in less common regions.
2. DM side book: Mass warfare, vehicles, stronghold building, monsters, more Planes info.
3. Player Side Book: I think this one is going to be a compendium of other Forgotten Realms regions much like SCAG, with subclasses. It could be a Planes book, but I think it might be Kara-tur and Zakhara.
4. Adventure Book: Based on the new subclasses and what hasn't been covered in an adventure yet... I think its going to be a Great Old One style adventure in the Sea of Fallen Stars region. Im also seeing more Feywild stuff lately, so maybe Star Elves of Aglarond and the Abolethic Sovereignty?