The Legion remix questline has some interesting tidbits.
You, the current champion from the current present day TWW WoW after having befriended Eternus in the Dragonflight patch questline and after having gone back with him to MoP remix, travel back in time to the start of Legion, swapping places with your past Legion self there (who is now presumably running around in present TWW).
You work with an Infinite drakonoid smith to take a crumbly sword and enchant it to make it look like your Legion artifact weapon, and then he opens a portal through time to replace your real old Legion artifact weapon.
Eternus muses that it might not have been the artifacts which saved Azeroth from the Sword of Sargeras' corruption that was threatening to kill her. Eternus also notes that the Bronze Dragonflight time police have curiously once again not shown up to stop us.
It's nice to hear a new subdued arrange of the climatic music from the final fight of Dawn of the Infinite as the Infinite Bazaar theme.