We are huge Star Wars fans here at CFK Blog so we decided to put a theory forward as to what Star Wars: The Last Jedi may be about.
Our theory more a less explains everything that has happened so far. Keep reading if interested. Note this is just a theory.
To begin, we think Luke and Snoke ran a Jedi academy together training a new generation of Jedi. One day the two friends found an old text that revealed the Jedi teachings were actually false and there is not only the light or the dark but that there needs to be a balance between the two. This shatters both men as their lives have up to this point been a lie.
Luke and Snoke both become Grey Jedi but while Luke gets the balance more a less right, Snoke veers to the dark side.
Snoke and Luke then slowly turn on each other, with Snoke pulling Kylo Ren to the dark side, using Darth Vader as a tool.
Luke seeing what has started to happen to Kylo, and then decided wipe the young and powerful, Reys mind and dumps her with a false memory on Jaku.
Upon discovering the missing Rey, Snoke is enraged and battles Luke. Snoke gets destroyed and highly injured in the fight, as Luke is far more powerful. This also somewhat will reflect the fight between Anakin Skywalker and Obi Wan Kinobi from Revenge of the Sith.
Kylo then turns on Luke (defending his master, like Anaken depended Palpatine) and Luke doesn’t want to fight back, because Kylo is a relative.
Luke gets buried in the rubble of the Jedi temple and the newly formed Knights of Ren, evacuate the near dead and crippled Snoke, who then forms the first order.
Note: This explains how Snoke and Kylo know about Rey and why Rey is screaming in the trailer (Snoke is removing Luke’s mind wipe).
It also explains, why Snoke is so injured (his injuries and hate then help him focus his dark side powers as well).
After both mindwiping Ray and dumping her on Jaku we now know why Luke is shocked to see Rey. Being more grey than dark it also explains why Snoke is not a sith.
Big twists in the film could then be;
1. Ray’s rage at Luke for wiping her mind, pushing her closer to Snoke and Kylo.
2. The reveal that the Jedi order was wrong.
3. Anaken Skywalker’s force ghost showing up at the very end of the film (Hayden Christiansen returns) pushing Kylo more toward the light.
An alternate but near identical version of our theory could be that Luke ran the academy, discovered there needs to be a light and dark side and invited the dark side user Snoke, to balance his light side teachings. Either way I suspect the two worked together, with Snoke betraying Luke, who then gave Snoke his injuries in retaliation.
Just a theory anyway.