1. Grand Admiral Thrawn: None of the Powers, All of the Wit
Star Wars: Aftermath -- the first Disney approved novel to take place after Return of the Jedi -- ends on a cliffhanger. Imperial Admiral and protagonist Rae Sloane is heard speaking to a second, unidentified admiral. Long-time Star Wars nerds theorized that this might be the newly canonized Mitth'raw'nuruodo, the alien commander with a name and pupils the size of grapefruits. Less obsessive fans probably know him better as Grand Admiral Thrawn, star of the titular Thrawn Trilogy and all-around individual not to be fucked with.
Debuting in Heir to the Empire, Thrawn pretty much went on to become biggest bad in the galaxy since Emperor Palpatine. This in spite of the Empire's very strong anti-nonhuman strictures, and the fact that he had no magic powers to speak of. This is just one of the ultimate reasons that the Chiss chap should be considered for canonical inclusion.
Star Wars has its fair share of heroes Force-free heroes. Han and Lando, to name just a few examples. Finn and Poe Dameron to name a few more. What it lacks is equally imposing baddies to balance the scales. Grand Moff Tarkin once wielded all the gravitas of a fully armed and operational Peter Cushing, but with the Death Star triggerman turned to vapor Thrawn has a void to fill.
Besides his ability to go toe-to-toe against superheroes with nothing but honed wit and starships, Thrawn is a presence. Of course one shouldn't judge a book by its cover (the one-Wookiee limb-removal company that is Chewbacca never hurt anybody that didn't deserve it), but come on. A handsome, blue man in uniform with glowing red eyes makes a distinctly sinister impression.
On the silver screen it'd be impossible to read his expression, and without the need for CGI or a static mask Thrawn would feel uncomfortably real as he traded tactics with one General Leia Organa.
Until, you know, she obviously beats him.
2. Mara Jade, Further Shades of Moral Grey
The Force Awakens did a fine job of shoveling in Star Wars' longstanding gender divide, but there's always room for more diversity in the kinds of characters the series could introduce. Rey is our newest hero, and Captain Phasma is repping the side of villainy in the coolest stormtrooper armor ever conceived, but the moral middle is still pretty much what it's always been.
On the whole, the original Star Wars expanded universe is about as diverse as the first two trilogies. That makes mining it for women of the bounty hunting and smuggling orientation a bit difficult. Just look at the proportions of this article, for instance. One exception is the oft-cited Mara Jade.
Jade was an assassin, smuggler, an agent of both the Empire and New Republic, and eventually even a Jedi Master. She wasn't just a character who walked on both sides of a conflict. She was a character who walked on every side, wall, corner, ceiling, and tasteful breakfast nook.
Beginning as a Force-sensitive spy for Emperor Palpatine -- the Emperor's Hand -- and ultimately wound up marrying Luke Skywalker. Her characterization cooled down a bit after marriage, but the beauty of recreating her for Disney's continuity would be the chance to ignore that wrinkle. And her trademark, 90s-as-hell leather outfit.
In fact, dump the marriage thing altogether and double-down on Mara's career as a free agent after the death of her previous employer took flying lessons from Darth Vader. Without the baggage of her ridiculous adventures with a would-be husband -- such as killing Luke's hilariously named clone Luuke -- Mara could well stand on her own as a Boba Fett or Asajj Ventress type, but with much stronger ties to the greater Star Wars conflict.
But seriously, we can leave the leather in the 20th century.