So there's this emphasis on the pre-war era in that trailer.

It could be just for the cools but how about this bs right here:

Maybe TIME TRAVEL will be involved, ow. You switch between the present and past, thereby not only witnessing the changes, but also (gameplay) overcoming obstacles and changing the future in order to achieve goals.

from what my friend said whos in the know so he says everything you do in the game will change it weather this is a time travel or just by the choices you make and all side quests will make small changes to also the karma system from what he says has gone and there is a law system in place but only if you get caught

Well, MY friend who's in the know says your friend is an agent of Galactic Overlord Xenu spreading misinformation to keep our thetan levels down.

Maybe you're the only inhabitant of Vault 111. Perhaps you play the intro in pre-war and when you gain access to the vault, you enter cryo-sleep and reawaken in the wasteland. Choices you make pre-war will effect the overall gameplay.