Some notes:
You wake up and the world is wrong
There is no war, there is no poverty, there is no disease.
There is only control.
Why do you have fleeting memories of a different world? One where the streets were not lined with drones. Where Force Users were not fitted with chips to detect its use. Where every home and workplace was not lined with sensors to watch for dissent. Where every news station, history book and syllabus was not controlled by (insert big bad here)
Freedom is a luxury that can no longer be afforded the citizens. However, the brutal wars which raged across the galaxy have been stopped. Science advances at an unprecedented rate.
Do you conform, or
Do you revolt?
In a twist on time, someone has altered the timeline utterly, but only a tiny fraction of the denizens of the Galaxy remember this. Revolutionaries start to be contacted by a mysterious persona, who starts to direct their actions.
If you choose to be a conformist, you'll be given prevent these acts of terrorism and restore order. HINT: the goodies are going to win and restore the timeline in the end...
For those that don't wish to participate, most simply don't remember the time line split ever happening and carry on in blissful ignorance.
In the run up to the event, writers will be able to submit technology for the alternate time line. These can be anything from commonplace items, massive stations, security enforcing drones, anything. They no longer have to conform strictly to the usual standards of the factory, as technology is far advanced in this alternative time line. The best will be used in the event.
For the codex, people may submit alternatives to common locations that can be completely different under the parallel universe's totalitarian regime. The best will be used at the locations for the event.