I think the theory about 4 Old World updates was pretty baseless and generated from almost nothing but reddit hype. Goblins and the Empire were the only factions in desperate need for updates, so I doubt anything more will follow. Even the Skaven are already too powerful, especially the last mouse (can't remember its name, it's the one riding that wheel of doom). In my opinion, there are only two remaining lord packs, the first to be released in Christmas and the second, concerning the orcs, sometime in the spring, probably before or just after Troy. Then, in summer, Warhammer III (and the 4 chaos deities! will be announced, in order to get published either in late 2020 or early 2021.
Nice point, I had completely forgotten it. To be honest, I'm a bit confused with all these announcements about additional, digital content, paid or free.