So the obvious themes in BFA are that of Death and the cyclular nature of life. Without going into too crazy of speculative theory about the grand scheme of things or how it ties into Titans/Old Gods… I wanted to focus on smaller players in the Universe.
We see Sylvanas burn down Teldrassil to upset the NIght Elves and destroy hope. This forces a mass evacuation and quite a bit of loss of life for the Kaldorei. Obviously Malfurion and Tyrande are super upset and we get the story that plays out in Darkshore. Pretty good, justified stuff - we see Nelfs at odds with Forsaken, arguably the most pro-life vs the most pro-death of races.
What we need - Kaldorei are long-lived race so I don’t imagine them generally having many children (we dont even see any night elf children iirc in game…yet). An obvious solution besides fighting back is they need to get busy - Stormwind needs to be full of expectant mothers and toddling elves! More importantly, Malfurion and Tyrande should have some kids of their own! The two have been married for over 10,000 years or so now - alot of which Malfurion was sleeping. Recently reunited, a good theme out of this devastation is Tyrande getting preggers. Ideally with twins because it would follow the theme of Illidan/Malfurion being twins (maybe girls this time).
We also see alot of death and destruction, mostly on the Horde side thanks to the Banshee Queen and her Banshee Prince. We see in the Warbringers Slyvanas dies to Arthas, looking back on a mother and child she failed to save. Again, this could be a theme - this gets into crazy fan theory territory - but its fun to speculate.
Slyvanas and Nathanos are extremely close and we see in novels they were actually romantically, physically invovled. Again, with theme-ing - what if that mother/child dying near Silvermoon to the Scourge is also reflected in Slyvanas? She goes into battle, recently having found out she is with child but prior to being able to tell Nathanos - Arthas takes this away from her just like he took away the other mother/child.
But why does that matter? Again, this goes into another crazy fan theory but I think it would make a great theme in the story. Arthas was the ultimate goal for Slyv to kill, once he was dead she felt no reason to carry on and thus we get the scene at Icecrown. However, she finds new reason to live after her suicide attempt there. After Varian’s death Anduin rises to be King. However, Blizzard has made several nods to how similar Anduin and Arthas are - the shot for shot cinematic at the Siege on Lordaeron . Jaina’s nightmare showing a newly modelled Arthas again, strikingly similar. The close bond Jaina and Anduin share… yep, I’m going with the Anduin Menethil theory with Jaina being his mom. We see Jaina reuniting with her own mom Catherine Proudmoore after being estranged and finding new resolve. We are introduced to Calia in Before the Storm and how Anduin remarks he reminds her of Jaina (who he sees as an Aunt but Calia could be his actual aunt) Taelia Fordragon -daughter to Bolvar Fordragon, current Lich King and possibly romantic interest for young Anduin. We have two heavy Lich King connections here - plus if you count Slyvanas being a new sort of Lich Queen herself.
This would make a fun dynamic between Slyvanas and Anduin and add even heavier layers of revenge - especially if Arthas took not only Slyvanas’ life but her potential unborn child yet Arthas’ seed lives on… a nice big circle that plays back into itself. Is it possible? I think the timelines allow such a thing to be so and yet to find any conflict in that. Some dislike the idea of Anduin not being Varian’s/Tiffin’s son and robs him from their relationship, but even if adopted the two’s relationship doesn’t really change much. I would assume Anduin would always see Varian as his true father. Jaina fills that parental role nicely since Tiffin died when Anduin was so young and the two have always been close despite ‘not being related’ cough.
So that is some fun speculation, please feel free to tell me your thoughts or add to this.