As for BfA and Shadowlands, yes they were absolutely aimed at cleaning up old and unresolved storylines. That's a large point I was making in my post. That WoD -> Legion and later BfA -> Shadowlands had a large emphasis on revisiting old lore, connecting to past stories and characters, and so on. You are also correct in saying Shadowlands was an "end of an era"-expansion, which is something I mentioned in my post. Danuser clearly said 9.2 closed one book and opened another, or something to that degree. That's what I'm arguing. Legion (at least for now) closed the book on the Burning Legion, Shadowlands (at least for now) closed the book on Arthas, the Scourge and all that business,
and 11.0 will (at least for now) close the book on the Old Gods, Elementals, etc,
You are absolutely right in saying DF is the start of something new. It is! Because Shadowlands was the end of something else! Notice the sharp constrast between Legion/BfA and then Shadowlands/Dragonflight. The reason for that is precisely because they are all part of their own trilogies (one might say of "books").
Note that I'm not suggesting 11.0 has to go all-in on elementals, nor am I saying that if they were to do so, we'll never see the elementals again. Demons are still around after Legion. The undead are still around after Shadowlands. We're not deleting those cosmic forces from the universe, merely concluding large stories focusing on them, going back all the way to Warcraft 3. New stories will open up in the future. We will meet characters like Illidan again at some point.
As far as I'm concerned, 11.0
likely involves Old Gods and/or the Void in a more primal form in some way, the elements and/or the Elementals in some form, and characters like Thrall, the Dragon Aspects, etc. Likely, some Old God or other notable character representing the Void will also be present. (Queen Azshara? Xal'atath? Who knows.) I also believe a World Revamp is likely. With the end of 11.0, I do believe we'll be seeing less of the above for a while. That's it.
Then when 12.0 comes around, I think it's plausible, but not for certain, that we'll have a very jolly and relaxed expansion where we follow the Pirate Armada and look for Avaloren or something to that degree.