Here are my night time deep thoughts on the direction of the movie having read stuff in and linked in this thread:
Generally speaking, the movie has to make sense to most people. It has to be easily explained & understood so that it can get to the point. In other words, it will have a very simple "I can see how things turned out this way" to the general audience. Nerds like us will have to rely on books n stuff for the deeper things (I know there is a book coming out soon that tells us exactly what went on after Jedi... at least in regards to the Empire/Rebels
The First Order: Much like how the Empire didn't just rise up from nothing, it converted from the Galactic Republic. All the storm troopers, star destroyers, etc. were all part of that military organization. I think the First Order is the same thing. When the rebels defeat the empire, they don't have the means to create a new entity, so they simply meld into what is already in place and go from there. Much of the military assets (people/ships) are retained to keep order. But the First Order and the "Rebels" of old are one in the same in a weird sorta way. Based on the trailer, it looks like whatever came from this union doesn't look much different than the old Empire.
This is also why "The Resistance" is a new name. Can't call them "The Rebels" because they aren't the same group... the rebels created the First Order. Most likely people like Leia are forced to choose sides. Right now I'd assume she's with the resistance, but who knows, maybe she's part of the First Order. Seems pretty obvious the galaxy didn't all of a sudden live happily ever after and this seems like a likely scenario. Hero's like Han & Luke were probably forgotten in the grand scheme of trying to put a working gov't after the fall of the Empire. And maybe they were glad to back away... that is until The Force Awakened and it's time to save the galaxy again.