Not sure if it was really a promise or considered an "important part" of the expansion but they did mention during one of the lore interviews during Shadowlands development that the sword wasn't as big a threat as before but it would get addressed in the expansion and I remember people then immediately started speculating everything from the Jailer was going to pull the sword from the planet and wield it in the final raid to Azeroth waking up in the final patch and using it to decapitate the Jailer.