So a while ago a developed something of a plot that I would personally like to see for the next two Star Wars films (obviously I know this will never happen) and tried to post on reddit not realizing the Star Wars subreddit is highly restrictive, so I decided to post here instead.
Keep in mind what follows is still not fully developed and will likely have lots of holes/oversights. Also, this mostly revolves around my new introduced character, I'm not really bothering with the other characters for now.
So my alternative storyline introduces a new character, "Vultus Ardan" (working name). Vultus was the son of wealthy aristocratic parents, nobles form their homeworld, and their world's senators in the Galactic Republic. Vultus was raised with the best education, as one would expect of a noble diplomat's son, and thus is quite familiar with the history of the jedi, and idolizes the old jedi.
Vultus was visiting Coruscant to be with his family for his birthday, in [insert appropriate coming of age, age here]. He was given a special gift from his mother on this visit, an old lightsaber, recovered from the jedi temple just after the Jedi were destroyed. He was departing the planet, and his vessel was just in orbit when The New Order destroyed the planet.
This obviously deeply enraged Vultus, filling him with all sorts of nasty emotions, and is also the first time he showed signs of being force sensitive.
Stuff happens and Vultus seeks out the resistance, hoping to join them in the fight against the New Order. His position on his homeworld is also important, as the resistance believes he may be able to rally their resources to support the resistance. He also receives basic training from Luke, assuming at this point he has returned from exile. He is very enthusiastic to help and to learn.
Vultus proves somewhat capable using the force, though particularly enhanced by his natural charisma, he is adept at the jedi mind trick, making him a perfect leader. He not only rallies his own planet to the rebel cause, but also makes the first steps in re-organizing and re-centralizing the Republic.
It soon becomes clear however that he has differences, and conflicts with the Jedi way of doing things. Ultimately he is powered by his anger and hatred for the New Order, and is very dark sided. This does not sit well with Luke/other concerned parties, but his power in the new Republic means they cannot force him away, as they need his help to fight the New Order. He particularly dislikes Luke's mercy, believing none of the New Order should be spared, as their crimes are too great.
At one point some of the new Republic forces come under attack by a massive New Order fleet. The Resistance believes it is a trap, or they do not believe they have sufficient forces to respond, and so choose to do nothing, with Luke advising them to be prudent. This drives Vultus into a rage, and he makes an outburst against Luke. He says he will lead the remaining available new republic forces into the battle, with or without the rebels and jedi.
Vultus' force mind trickery becomes clear in its ability to manipulate even large crowds, as the rebels, formerly unanimous, become divided, and some follow Vultus into the battle. Stuff happens! In the battle.
Next major plot point I have is that Leia/other parties attempt to bring Kylo back to the light side. For a moment it seems like they might succeed, but Vultus kills Kylo, unable to forgive him for his part in the destruction of Coruscant. This is the final straw. The Jedi/Leia cannot forgive Vultus and order whatever forces they can to retreat from the battle, which they are losing. Most of the new Republic fleet is destroyed as the rebels withdraw and ultimate strategic victory for the New Order seems inevitable.
Rey then contacts Vultus independently and asks for his assistance making an attack directly at Snoke to cut the head off the snake so to say. He agrees, though he has come to despise her and the Jedi for leaving the new Republic forces to die in the battle. Eventually they encounter Snoke, engage him in battle, and lose. Snoke senses the dark side in Vultus and attempts to recruit him, ordering him to kill Rey as proof of his loyalty in a very dark sidish manner. He seems for a moment as though he will, but kills Snoke instead. Ultimately his dark side powers are fueled by his deep hatred for Snoke, and this allowed him to avoid being manipulated.
He allows Rey to flee, then uses his force mind tricking powers to convince a group of storm troopers that he is now in charge of the fleet. He takes control of Snoke's capital vessel then orders all of the remaining New Order fleet to submit to his will or be destroyed. He takes the name "Darth Retribus" refounding the sith, and takes his fleet to hyperspeed, disappearing into the depths of space.
They shall call me, Draglide! The thread killer!