I would finish BfA in two parts.
Patch 8.3: Battlefield: Ashenvale:
Ashenvale is in due need of an update (please get rid of the Ashenvale Thunder Peak volcano already). And this makes an obvious continuation to the Darkshore Warfront storyline, since Ion said the Night Elves were preparing to get in striking distance of Orgrimmar, and Malfurion did send the message meant to tell Sylvanas that we are coming. On top of that, if we are really going to see an end to the faction war after BfA, we need both Saurfang and the Horde to demonstrate acts of atonement for the War of the Thorns so the Alliance can see the Horde as not purely evil.
Patch 8.4: Siege of Stormwind:
The Horde and Alliance make it to Orgrimmar only to find that Sylvanas is no longer there. She has already left to attack Stormwind, and has taken all her loyalest Forsaken and Horde soldiers (lets say some of the raid bosses even admitting to having been manning the catapults and using their magic to burn Teldrassil) and takes the city in a surprise attack, going to execute her final plan of razing and raising Stormwind even without the rest of the Horde. Alliance and Saurfang and the Horde rebels make their way to Stormwind and save Anduin and the city and defeat Sylvanas together. This would place the Horde and Alliance in a position of nearly nonnegotiable peace, and with having started atonement with the Night Elves before this, there’s no one to mess it up any more.
Sylvanas escapes again, but we kill her later, like we did Garrosh.