The Mandos are pretty great. Jet-pack space-cossacks, what's not to love? They're one of the bits of the EU I really hope they try to reconstruct, to some extent or another.
Dachs didn't like them at all, but he seems to have vanished, so there's pretty much a consensus now that jetpack-wearing space Cossacks who consider armor an integral part of their culture are
really cool.
They, and some of Matthew Stover's works, especially
Shatterpoint, should stay. That was
Apocalypse Now in space starring Samuel L. Jackson. Awesomeness overload.
Now, Disney and Abrams know that the prequels were widely panned (though I have to admit I really liked
Revenge of the Sith), and reportedly Abrams has striven to make
The Force Awakens more true to the originals. I just hope that he doesn't go overboard and just rehash the old recipe of good Jedi+evil Sith=Star Wars. While I wouldn't get rid of the Sith, I'd add more moral ambiguity. I also hope that he tries not to overdo the tired trope of having the protagonists being the descendants of the last protagonists. That creates a kind of hereditary, almost aristocratic idea of characters. I mean, it's a trope that is basically appealing, since it maintains continuity while also showing change over time, but it suggests characters' birth is the main determinant of their importance and traits, even though the son or daughter of a war hero or famous smuggler might just want to be an author or something mundane and have little in common with their parents. And the whole legend of a protagonist learning about their heroic ancestor and deciding to take up their legacy is also a tired, aristocratic trope.
I'm not expecting Abrams to shy away from this cliche--I figure he'll probably follow it--but it would be nice to see some very different characters, while maintaining enough links to the familiar past.
It would also be pretty interesting if the new movies might explore the theme of the old ways and people struggling with their obsolescence as new ideas, people, and technology take over. Imagine if the new Star Wars universe is like Traitorfish's example: decentralized, more chaotic, and so on. The old generation might reminisce about how they heroically fought to topple the evil Empire, but they'll be relics of an age of clear morality and clear enemies surviving in an age of ambiguity and uncertainty, where nothing is clear-cut. Their kids will listen but will make their own path, since the game has changed. Their grandkids will ignore them as fossils whose accomplishments and lessons have no application in the present day.
There could also be technological obsolescence, such as the rise of droids. The CIS was able to crank out absolutely overwhelming numbers of battle droids, automated vehicles, automated fighters, and even automated ships very quickly and easily. They don't need twenty years of rearing and training to be useful, they don't need food, water, or payment, they don't rebel or feel fear, and they aren't as easily destroyed or incapacitated. They are easily repaired and readily upgraded in both hardware and software. Their reaction speed and accuracy can far outclass any human's, if they are properly designed. The big problem of the CIS was that it was often poorly led, that the droids' AI was generally awful, and that, of course, it was destined to lose by the fact that the Empire had to emerge out of the Clone Wars. Yet people in Star Wars seem perfectly capable of designing intelligent and creative droids--IG-88, C-3PO, and R2-D2 spring to mind--which undermines the argument that droids can never be creative enough to fight effectively. Neither is your average, frightened, inexperienced infantry private, but people don't seem to notice that. Anyway, an army of droids, if smart enough to take cover and exploit their advantages, and if led by capable organic beings, would have a huge advantage over any other kind of army. Even Jedi skill can be overwhelmed by sufficient numbers, especially if complemented by skill, and organic troops would increasingly lose ground as the sensible armies picked droids instead. It would be interesting to see how characters react to the growing outdatedness of their skills, stories, and lessons.