they literally wrote the script like this:

Make a Finn a super soldier who is trained to kill Jedi who once he turns good still had nightmares of the atrocities he's committed. Thus he spends the rest of the franchise trying to atone for his sins
This way you can have Rey as the pure spirit who brings out his goodness.
Also you could keep the Starkiller base. Except this time the big twist is it's a trap. It's whole purpose is to lure the Republic forces (nix that resistance crap) only to blow up the planet destroying most of the Republic forces
Also make the First Order it's own thing with own identity rather than an empire knockoff. Like Communists vs Fascists.