It's definitely possible, and I think it allows for a better conflict storyline, better than just bringing back old enemies or the Sith.
I have a similar theory. In the natural progression of civilization it goes from barbarianism, democracy, republic, empire, and then back to the start. The Empire represented death but was still an organized civilization. There was still an order there...and it was dominating. Once that dictatorship government is toppled, the next step in the cycle wouldn't necessarily be a New Republic, it would be lack of civilization, lack of order. In other words; chaos. All of the unified agents that toppled that former state, that Empire, could end up fighting each other for control.
We could easily have something play out as follows; 30 years after the toppling of the Empire, remnant governors still maintain control over their local systems. They act like mini warlords. It could be a hornets nest of complex border disputes and, much like what happened after WW2, those remnant Imperial systems could end up like Berlin, Germany or even Cuba. They could be forced behind sectioned off "Iron Walls", where those systems now lay in complete ruin.
Perhaps when the story opens, the Rebel Alliance, or whomever is in control is dealing with trying to get some of them back into the larger order. Perhaps they're chasing down fugitives still. Perhaps those Governors are totally resistant and despite their ruining economic state, keep their control. I'd think it would really interesting to have some of the old Imperials come back to the good side. We could have one of the main characters be an Imperial, or a stormtrooper who switches sides. It would be a symbol of how the Empire, now defeated and the Darkside itself is now returning to the Light..which was made possible by Luke defeating the Emperor. That act, returns the lightside to dominate and EP 7 begins with that progression.
We could also introduce another element, one that occurred with Rome. Imperial Rome was toppled due to many factors, including economics, a scattered military, new religious orders coming into existence and foreign invasion. The outer flanks of the Roman territory were invaded by Barbarians. The Barbarians invaded and it broke up that Empire ( ** All of this is pretty abridged version of history, forgive me)
Without a strong governing structure in place (as wicked as the Empire was they held the Galaxy in place) and without a new governing body to immediately take over, the Galaxy would be tremendously vulnerable. Any outside army could invade and take over outlining systems easily.
This also fits in quite nicely with a more spiritual Jedi Luke mission. Luke wants to bring about a new civilization and much akin to how Christianity was built up after the fall of Rome, the New Jedi Order/Spiritual Force could fill in that role. Luke/Jedi/Lightside vs Utter Chaos/Barbarianism.
And with that, you could also introduce Luke gathering 12 new Jedi Knights to form a new jedi council. Imagine a scene where 12 individuals land on some planet all because they 'felt' the force calling them to this place. There they each climb the mountain to meet the Master. It could even be reminiscent of King Arthur. Luke could be a Merlin like figure, where he's looking for a "good and just King", a King Arthur type, someone truly deserving for rule. Someone to lead the people and usher in a new democratic state and defeat chaos, and the threat of lack of civilization itself.
There's a lot of potential. Much, much more than just bringing back the Sith, or the Emperor, or having Leia falling to the darkside.
