SPECULATION Where are the Sith??

There's no more Sith in the canon after the death of Vader and Palpatine, Anakin fulfilled the prophecy, Snoke and Kylo are not Sith.

 

The Sith are extinct, but their legacy continues through Kylo Ren and Snoke, the mirror of Vader and Sidious respectively. Amassing dark side power, red lightsabers, galactic conquest, Imperialism, kyber-crystal powered superweapons, Jedi destruction etc, shows their legacy lives on. The only significant departure so far is the Rule of Two, but a similar relationship prevails. Rather than re-writing the Sith and the Empire from scratch, Kylo and Snoke seem to respect its traditions, but at the same time trying to remove its inherent flaws.

Kylo, a quasi-Sith, emulates the traditions of Vader and seeks to fulfil his legacy.

"A dark side warrior with a mysterious past, Kylo Ren was neither Jedi nor Sith, but a product of both sides’ teachings." (Databank)​

Snoke, leader of the First Order, is rebuilding the Imperial legacy that Sidious began.

"In the galaxy’s Unknown Regions, former Imperial officers, nobles and technologists plotted a return to power, building fleets and armies in secret. This movement became the First Order, ruled by Supreme Leader Snoke, and is now ready to reclaim the Imperial legacy." (Databank)
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The TFA novel paints the picture that Snoke was a keen admirer and observer of Vader and the Empire. Would Snoke allow Kylo's Vader fascination if he fundamentally disagreed with the Sith way? He praises the accomplishments of "Lord" Vader, ruing his one mistake that led to the Empire's destruction:

"Such a foolish error of judgement. A momentary lapse in an otherwise exemplary life. Had Lord Vader not succumbed to emotion at the crucial moment–had the father killed the son–the Empire would have prevailed." (TFA novelisation)
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Snoke also dislikes how historians view the fallen Galactic Empire. Snoke defends the Empire's strategy and defends the claims against it being too arrogant (I read that from the novel as him defending the Emperor):

"I watched the Galactic Empire rise, and then fall. The gullible prattle on about the triumph of truth and justice, of individualism and free will. As if such things were solid and real instead of simple subjective judgements. The historians have it all wrong. It was neither poor strategy nor arrogance that brought down the Empire." (TFA novelisation)
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Unlike Vader, Snoke hasn't discussed Sidious, but given that Snoke has built his First Order much in the traditions of Sidious' Empire, given how Snoke defends Sidious' Empire, given how Snoke admires Sidious' apprentice, I would guess that Snoke comes from a similar background as Sidious too.

"As the Supreme Leader of the First Order, Snoke stood atop an evil regime that mirrored many of the dark traditions of the Galactic Empire. As a striking example, Snoke was flanked by crimson-clad guardians, loyal protectors encased in the ornate armor ready to defend the Supreme Leader from any threat." (Databank)
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I think Snoke has some previous connection to the Sith as well. He must have. He has observed and learned from the Empire, he must've observed and learned from the ways of the Sith to some extent too.

 

Nope, there will be no mention of the Sith in the ST. Nada

But... I think he has learned from the Emperor and has a somewhat level of respect and admiration for him. I doubt the movies will go into this though.

 

No matter what Snoke's real identity is, he is most definitely an ancient Sith - and his former life will be explored in a new trilogy taking place 800-1000 years before TPM.

That's my guess.