Alright, some theorizing (much of which is probably repeating what others ITT have gathered but I'm not about to read all 380 posts):
Netherrealm as primary antagonist is wrapped up at the start, just like in MKX. Then Kronika barges into the story and takes over as Big Cheese, putting the royal revenants back into jobber status. It seems like she makes her grand entrance in Kotal's Koliseum, summoning all the past timeline characters in one fell swoop. So the time travel seems to be limited, for now, to bringing people from the past into the future (and not vice-versa or anything). But that limitation doesn't explain some of the game's stages looking like altered history (Shang Tsung's Island and Goro's Lair), so perhaps time travel will be explored in more ways later in the story.
Subsequently, a battle understandably breaks out in the Koliseum, because she brought forth good guys as well as bad guys. (Surprisingly she doesn't have control over their motivations, and doesn't/can't poof the good guys back when they decide to side against her.) Kotal is pissed (and pissing himself) and sides with Light Raiden for obvious reasons. At some point, it looks like Shao wins over the respect and command of Kotal's forces. Shao v. Kotal will be a major plot thread and I'm salivating right now.
The Erron brought in by Kronika... Erron's new leather jacket is bitching, by the way.... is probably a younger Erron who works with Kano and the Black Dragon. Explains him jobbing for Shao and not Kotal. Kotal's Erron is MIA in the trailer - possibly made short work of in a duel with his younger self? Also explains Erron attacking the SF hangar with custom goons, as well as his fight against young Sonya in the Cage fam assault on BD Klub. With two Errons probably running around, and one employed by Kotal and therefore working for the side of light, this may mean we get an Erron chapter and I'm all out of saliva.
Past Jade seems to have a huge role in Outworld, running from/leading tarkatans, and joining Kotal in some fantasy side quest romance novel with a pony.
The most curious shot to me is Dark Raiden and the kombat brats running out of a portal in an Earthrealm desert. The lighting is different from the SFDC stage so I'm not sure it's them coming to the rescue of the Johnnys. It looks way more climactic than that, but it's weird for the climax to be in a rando desert.