Oh well, since you asked-
-Cracks knuckles-
Prelude; I simply wouldn’t have killed off Vol’jin at the start of Legion. Rather than some half-baked mumbo jumbo ‘forshadowing’ that we got, which was a huge nothingburger tbh, I would take the chance to introduce Bwomsamdi now, and have him, Vol’jin and Sylvanas have a talk on the threshold of the Other Side.
Bwom points out that, while usually he’d be more than happy to nab a Warchief’s soul, having the entire world dead and their souls ground down into Fel Dust is ‘bad for business’. Instead, him and Vol’jun cut a deal; Vol’jin will bind himself to Bwom and him alone (much like Rastakhan did in how BFA turned out), while haggling to allow the Shadow Hunters the choice to do the same, making a jibe on whether Bwom would be happy being as much a tyrant as the Legion, which ultimately he relents on while laughing it off, as he does.
Vol’jin is purged of the Fel wound (a little painfully; it’s still death magic and Bwom, at the end of the day) but survives. Since he’s bound to Bwomsamdi, he doesn’t want to have that influence the Horde, and still suggests that Sylvanas takes the mantle of Warchief. At first she wants to refuse, until he points out she used to be a Ranger General, and is used to defending ‘her people’. Although she counters that she failed that already, Vol’jin notes she has a second chance here. End result, she accepts, albeit begrudgingly.
So! We’ve just come out of Legion; the world has been Sword Stabbed, we’ve drained the artefacts to remove the Fel poisoning, the Earthen Ring and Cenarion Circle are doing their thing, yada yada. The factions have been working together so long, surely peace is on the cards now, right?
Well, wrong. Anduin is now King, but he’s taking advice primarily from Genn (Velen taking the time to see to his people and also a damn break, given they finally beat the Legion) and the likes of Admiral Rogers. Turalyon may well be in the background too. Ultimately, though, the advisors are watching the Horde (or, rather, Gallywix) grabbing as much Azerite as they can, experimenting with it, etc.
Genn, being Genn, insists that it’s a matter of time before the Horde, especially under Sylvanas, rally and attack them. With multiple voices urging it (including the Jaina we got a good glimpse of in the Warbringers trailer), Anduin agrees to their plan. The Seige of Lordaeron happens pretty much as is, though tbh we could cut the whole Saurfang arc or at least this segment of it.
With the Horde on the back foot, certain Commanders urging for them to strike back and secure Kalimdor against any possible attacks, and Gallywix offering his new armaments (at a reasonable price, of course) Sylvanas and the other leaders conclude that it’s safer for them to push Alliance forces back before they march on Orgrimmar, Thunderbluff, etc. They can still feint towards Silithus - after all, that’s where most of the Azerite mining is going on - and then we get Darkshore as a retaliation to Lordaeron.
The Old God angle should be seeded early on for the arc to work; the War of Thorns starts out pretty much as previous, but the fighting gets fiercer and fiercer. Personally, I’d have had Sylvanas and some of the other more established Forsaken (not all) be immune to the Whispers, so instead of being villain-batted for no good reason, you have them watching as their troops get more and more bloodcrazed.
The end goal was simply to force the Kaldorei off the mainland, and then set up a naval garrison and shore battery to keep watch. Instead, you get Sylvanas watching as Azerite empowered rocket batteries, mages, etc launch at Teldrassil. No more ‘intercontinental’ Demolishers, Azerite was the perfect tool to use here and make sense, as well as show how dangerous it is when misused.
The rest of main BFA can continue quite similarly, though personally I’d look at whether it would work better not having Zul go off the deep end?
Rastakhan and Rezan I would change; rather than having Rezan get offed and turned into a Dungeon boss, I’d instead use Vol’jin’s link with Bwomsamdi to offer the Horde a very useful Favour Owed; save Rezan’s soul and restore the Loa of Kings, thus saving the King, and putting the Zandalari in their debt. Also a win for the Darkspear, where the ‘lesser’ tribe actually proves potent enough to stand on equal terms.
Rather than petering off into “Oops, we did a violence” though, the culminating arc would be the realisation that draining all this Azerite is leading to the weakening of the Old Gods prison. The realisation is had that the Alliance and Horde are both being driven to more and more violence by the incessant whispers, thus using more Azerite, spilling more blood, and fuelling a downward spiral. Azshara, having acted through the Tide Sages and the greedy mind of Gallywix and his cronies, reveals herself with full arrogance and evil laughter as befits her normal style.
I haven’t figured who the ‘Final Raid Boss’ for BFA would be in my version, but we wouldn’t see Nazjatar and related environs until the next expac. We’d likely have Gallywix and Ashvane, fully hopped up on Azerite and Old God Whispers, as bosses somewhere, and although the factions would manage to stop them, the finale would reveal that it was too late; Azshara has at least partially broken the seal on the Old Gods prison, and now we’ve got to do something about that.
Lead into the Naga expac, before we finally have to deal with the Old Gods resurgent and Nyalotha in the second expac. Could always hint at the Void Lords as the greater evil behind the scenes, as well as if we did defeat the Old Gods that being enough to finally draw their attention.
No villain-bat for Sylvanas. Azshara getting to be the Big Bad properly, as well as having the showdown between her and Tyrande that has been so long overdue, as well as possibly mending relations between the Night and Blood Elves, at least a bit. Saurfang could still have his ‘go out in a blaze of glory’, maybe with Anduin and Wrathion throwing him their respective weapons when he YOLOs at the Avatar of N’zoth, as Muh Honour overpowers the Void Whispers long enough for him to do some damage.
Regardless; Not. Shadowlands. Cos that was stupid.
/Rant