This has all been done before (Canonization I mean).
A long time ago in a galaxy far far away there was the Original Trilogy - Star Wars, The Empire Strikes Back, and Return of the Jedi (I still refuse to call them Episodes IV, V, and VI)
These were like the 10 commandments - Thou shalt NOT write stories that took place before Star Wars, as George had a plan in mind to revisit a prequel saga. Thou shalt NOT write stories after Return of the Jedi.
Then a funny thing happened. He started making money by the boatload on licensing and toys. He opened things up slightly.. Comics were made that took place during the movie period (Galactic Civil War) - Marvel had these rights. Then he licensed out authors to write stories as well - Splinter of the Mind's Eye takes place between Star Wars and Empire. There were 2 series that took place before Star Wars, and told a back story about Han Solo - Han Solo at Stars' End, Han Solo's Revenge, and Han Solo and the Lost Legacy. There was a series about Lando as well - Lando Calrissian and the Mindharp of Sharu, Lando Calrissian and the Flamewind of Oseon, and Lando Calrissian and the Starcave of Thonboka (I still have my original Hardcovers of all 6 of these books..).
Everything was good for a time, but anything further back than these 'prequel' series was verboten. Anything written that took place after ROTJ was also off limits. Then, in the early 90's, Lucas thought to himself, maybe I'll open up things to be written that take place after ROTJ, and thus Timothy Zahn (Praise Be Unto Him) created the Thrawn Trilogy, and thus the Expanded Universe was truly born.
What came after was a deluge of comics - with licensing deals moving to Dark Horse, Books moving from Del Rey to Bantam, Video Games and the like.
NONE of these were considered canon. Lucas had always stated that the Movies stood on their own. Then a few years later, these rules were slackened a bit. Certain things had varying degrees of canonicity (is that a word? Let's say it is..)
Movies have always been number 1, Books 2, Comics 3, Video games fell in last..
Now that Disney has taken the reins from LFL, they haven't discarded anything, they've just backpedalled a bit in what they consider to be canon. Movies are considered canon only. Anything that is EU MAY be used in future movie projects. This was done so that JJ, and whoever comes after him isn't bound by the EU, and has some freedom. Are Han and Leia married?? Maybe. According to the books they are. According to the books, they have a few kids too. But JJ doesn't have to go by the books. He can if he wishes, and once he does commit it to the screen, it shall be forever set in digital stone as canon.
So, after this long winded rant, does this mean that FFG can't use EU stuff? Hell no! They can likely do whatever they like - Disney won't care, as long as they make money from it, and it doesn't step on the toes of upcoming releases.