What is the history of the Sith according to new Disney canon?

Question

With the proverbial death of the EU, what are we to make of the history of the Sith? All of us who have been readers and followers of Star Wars have known now of the Sith for years, and the history of the Sith dates back thousands of years into the past.

My reason for asking is this: If Disney no longer holds the old Sith culture and history Ccnon, it could de-emphasize this long term legacy that the Sith had in the galaxy. It appears that the new universe is focusing on a new Dark Side cult, the Knights of Ren. As a long time fan, I find it hard to remove myself from a universe so etched in the duality of Jedi vs. Sith, even though the deeper idea of Light vs. Dark carries no labels.

Certainly then, no Naga Sadow, no Exar Kun, no Darth Bane,... so what now?

Answer 1

Actually, rejoice, because YES Darth Bane. He was in Clone Wars cartoons, so he's part of Disney canon.

This is one of the cases where Wookieepedia is actually an awesome resource to determine the breadth of information and list the primary sources, so I will heavily leverage it as a starting point. Here is the extent of details of New Canon history of the Sith:

• Marvel's new Star Wars #9 comic: "Showdown on the Smugglers' Moon, Part II" says that the Sith (called "originally, brothers in the force" of the Jedi) were born during something called "the Hundred-Year Darkness".

  

• Sith article @starwars.com as of 11/2014)* states the origins:

  Thousands of years ago, a rogue Jedi had come to the understanding that the true power of the Force lay not through contemplation and passivity. Only by tapping its dark side could its true potential be gained. The Jedi Council at the time balked at this new direction. The dark Jedi was outcast, but he eventually gained followers to his new order.

• The same article tells - high level - the familiar story, how Sith would in-fight each other till Darth Bane instituted the Rule of Two.

• Moraband article @ Databank details the homeworld of the Sith order, which appeared in Clone Wars "Sacrifice" episode.

  An ancient homeworld of the Sith Order, the planet was abandoned after repeated devastation following multiple wars. The red-sands planet is home to the Valley of the Dark Lords, a corridor of ancient monuments that serve as crypts for the Dark Lords of millennia past. The largest monument contains the sarcophagus of Darth Bane, founder of the Rule of Two that helped shape the modern Sith Order. This temple contained a massive execution chamber, where the ancient Sith Lords would sacrifice Jedi prisoners. Yoda ventured to Moraband near the end of the Clone Wars on a spiritual journey initiated by the disembodied voice of Qui-Gon Jinn.

• Death Star Superlaser @Databank says that as part of their wars, they built superweapons in the mold of Death Star:

  According to legend, the ancient Sith used massive kyber crystals to create superweapons; during the Clone Wars, the Geonosians revived the superlaser design

• Star Wars: The Clone Wars – "Escape from Kadavo" episode, according to Wooliepedia, tells us that

  The Sith built empires on the backs of their slaves

  ... while "The Big Bang" episode says (according to Wikia)

  fought wars against the Jedi for control of the galaxy

• According to James Luceno's "Tarkin" novel, the Jedi Temple on Coruscant stood on top of 5,000 yer old Sith shrine:

  The two of them were in Sidious’s lair, a small rock-walled enclosure beneath the deepest of the Palace’s several sublevels that had once been an ancient Sith shrine. That the Jedi had raised their Temple over the shrine had for a thousand years been one of the most closely guarded secrets of those Sith Lords who had perpetuated and implemented the revenge strategy of the Jedi Order’s founders.

  Even the most powerful of Dark Side Adepts believed that shrines of the sort existed only on Sith worlds remote from Coruscant, and even the most powerful of the Jedi believed that the power inherent in the shrine had been neutralized and successfully capped. In truth, that power had seeped upward and outward since its entombment, infiltrating the hallways and rooms above, and weakening the Jedi Order much as the Sith Masters themselves had secretly infiltrated the corridors of political power and toppled the Republic.

  Save for Sidious, no sentient being in close to five thousand years had set foot in the shrine.