Kairoz's experiments on the Timeless Isle to return the Bronze Dragonflight's mastery over time have paid off, but at a cost. Ingesting a processed version of the epoch stones allows a dragon to regain their full powers of pre-Cataclysm, but it causes their minds to become weak enough that they can be more easily corrupted by the Old Gods. This side effect, however, takes several months to set in, so a sizeable portion of the Bronze Flight have accepted and used the method before anyone notices what's going wrong.
Players now find themselves at a point in Azeroth where the Infinite Dragonflight have begun to rise. Several zones take place in the past, one or two in the present. For example, one leveling zone is Elwynn Forest during the first war, where the Infinite Flight have tried to change events so the Orcs never destroyed Stormwind. You quest throughout the zone to stop the Infinites, to uphold history, and the zone's story culminates in a raid on Stormwind where you prevent the Infinites from interfering so the Horde can accomplish their destiny.
Side-antagonists can be misguided members of the Alliance (or even the Horde) who believe things could be better if history were changed.
Essentially, the story for each zone would involve preventing the Infinites from changing things, whether by travelling to the past to stop them, or stopping them in the present so they can't provide reinforcements to themselves in CoT dungeons we've done in previous expansions. Protect our past selves by fighting in the present. Scenarios in the form of 'time quakes', slivers of history becoming accessible throughout Azeroth, are another method of visiting and protecting Azeroth's history, as well as seeing some old removed content in a new context.
The final raid would be deep within the Caverns of Time; within the Hourglass. In this zone, time is non-linear, and spiritual fragments (not the real things, echoes) of history are scattered throughout. It represents a desert, with notable places and events taking place. To the south is Stromgarde, used as a setting for several boss fights. To the north is the kingdom of Zandalar. That sort of thing.
The raid culminates with meeting Noz at the Nexus of the timeways, the core of time, which was revealed to be getting weaker throughout the expansion due to corruptions to history. As we approach, Murozond suddenly appears, crazed, and fights against us. With Noz's help, we manage to weaken him, only for him to disappear into the timeways, for our past selves to eventually meet and defeat.
The final cinematic of the raid involves the Nexus buckling under the pressure of the fight, and Noz reluctantly revealing he knows how to save it, apologising to the mortals, and stepping in to the whirlpool of history. He is obviously agonised, his consciousness being spread thin across all of Azeroth's timeline, and the whispers of the Old Gods all throughout history turn to shouts delivered directly to his ears. The Nexus is stabilised, and Azeroth stops having its little time quakes, but Noz staggers out, looking up at the raid as his skin slowly turns from bronze to the Infinite's colour scheme. He yells that he has been exposed to all of time, every history, every moment, and that he must change things so events he now believes will happen will not happen.
Too mad to be able to distinguish between what he saw and reality, the newly formed Murozond disappears into the near past, obviously to fight out raid.
We leave the Hourglass to discover the time quakes have lured the Legion to Azeroth for the next expansion.