I wonder if they will play an angle where Caldoran is from the current timeline in “modern WoW”, was sent back in time somehow and tried to change the future where the Scarlet Crusade had the means to prepare, withstand and ultimately defeat the scourges invasion of the Scarlet Enclave. By ensuring they had the Ashbringer. The weapon that would shatter Frostmourne. But also other methods. Putress was the mastermind behind the Forsakens “new plague” after all. Which was developed first and foremost to be a weapon against the scourge. Hence why he was “recruited” by the crusade. Also using the light to resurrect the dead would allow them the means to deny the scourge corpses to raise. Thus depraving the scourge of their biggest asset. They can’t win a war of attrition when the other side also has an infinitely risen army. As seen with the proto-drake and the Reborn council encounters.
Sure the Lich King cannot be killed unless he is at the Frozen Throne, but deprived of Frostmourne, Arthas is just as powerful as a regular Death Knight. Hence why Wrath put such a strong emphasis on Frostmourne and it was the lore reason behind the Frozen Halls dungeons ultimately. Try and steal Frostmourne from the Lich King.
Basically view Caldoran as WoW’s version of Klesser from Infamous. But the key lesson in both these cases… One often meets his destiny on the path he takes to avoid it. By attempting to prevent a grim future, they instead path the road that allows it to happen.
Given that a SoD original character appears in Undermine and references their role in SoD makes me think that we will see more overlaps with SoD and retail. Maybe in Midnight we encounter Caldoran and he escapes through a time portal.
Now that I think about it, if Caldoran and the Crusade were successful in stopping Arthas at the scarlet enclave, then were would be no real reason to go to Northrend. Well outside of the Nexus War maybe. But there is a key individual that would love to see the Lich King defeated. After all, they had tried to ensure that happened in the past when a… friends servants aided a certain demon hunter.
Blizzard did say Dawn of the Infinite would not be the last time we see the infinite dragonflight.