"One book of the Warcraft saga" [that was started decades ago]. That was what they meant and no, they've not been talking about the Sylvanas storyline. Shadowlands was the climax of the Warcraft franchise as of now, dating back to the OG Lich King etc. Dragonflight supposedly starts the "new" book of the saga.
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Ok. Then let's wait for all these future expansion they're making use of all of this threads they've going on. Doesn't change the fact that the Jailer storyline itself had no effect on the world at all. The things you've listed are mostly minor side plots they have in every expansion, side plots that more often than not are abandoned instead of used in the future.
I think this discussion is pretty pointless as it's been proven time and time again how terrible and damaging the Shadowlands plot is for the franchise, we don't have to go back to that. So let's focus on all the grandiose Dragonflight news.