I'm not very knowledgeable with stuff outside the films so here goes.
Many years have passed since the fall of the Empire. Han and Lea are happily living a peaceful life on Tatooie (Well, this planet's been an important place in the series). Luke has basically vanished from trace, on some quest to find an apprentice to continue the Jedis. One evening, Luke returns unannounced to the Solo residence. He informs the couple of a new treat to the Galaxy (A sort of Agents of the Empire, whatever.) taking over the place, constructing a new space station that'll make the Death Star look like a kiddy toy, and they're out to kill those that were part of the Rebels and played a hand in destroying the Empire, including the Solos. Having witnessed a genocide on the Ewok homeworld, Luke's purpose is to take Han and Lea into hiding.
So after some action and a case scene on that Land Speeder from A New Hope after some bad guys show up (I think this film will use new foot soldiers instead of Storm/Clone Troopers or those god awful CGI robots from the prequels), the trio arrive in that town from A New Hope (I don't know the name of everything in SW so please forgive me) and after an excuse for that catchy bar music later, the three arrive in a sort of garage for space ships where we meet the Solo's son and his friends who own the place. Han and the son don't see eye to eye much because Han wasn't around much when he was growing up or whatever. We also see Chewie, who works as the boss of the garage and a lot greyer, as well as a rusty R2D2 and C3PO (Well, might be fun to see them old and rusty). We see the Millennium Falcon at the back of the garage, either looking better then even or worse then "a piece of junk".
So eventually, they get going, space battle, end up on the evil space station, and work out how to stop them and inform the proper people what they're up to for a big climatic space battle, as well as Luke and the son getting into X Wings (Or NEW Wings XD) to join in, and meet whatever villains Disney hope will upstage Mr Vader and co.
The next 2 films explore the reforming the Rebels (With appearances like Lando and whatnot), the ever growing new villains, Han's relationship with his son, as well as Luke seeing some "potential" in the young chap and his friends as possible new Jedis.
So yeah, a mix of nostalgia and new thrown in, as well as passing the torch so to speak. Most of film I just thought up on the spot, but meh, can't refuse a chance to own SW in Steel (Edited or not) for free.
