Kylo Ren would have been a much better character as Ben Solo.
Then I would imagine that the big bad could have been a a new sith rising up in strength as the republic works to get the galaxy cleansed from the empire. Luke could have been similar to the role of QuiGon Jin and went from place to place breaking up the former empire causing trouble.
We would have been able to see Luke perform amazing force abilities, Kylo could have been like Obi Wan in the original and they could have re-established a new Jedi council with Asoka.
Hell, you could even start a new rebellion with some former empire higher ups and brought a new civil war to forefront with the jedi fighting along side the mandalorians to squash it. Think Thanos and the Avengers type of showdown in the new movie 6.
1st movie - former empire is seizing control of the outer rim. Luke is training Kylo. Asoka and Bridger who has returned is leading a fight against Thrawn who also has returned as the new big bad. Thrawn and his two sith apprentices are forcing worlds to choose sides once again. Thrawn has the remnants of the empire's fleet and is performing terrorist attacks across the galaxy Guerilla Warfare style. Luke and Thrawn have a drag out fight. Thrawn survives after a loss that was a near victory.
2nd movie - Thrawn has a devastating attack on the new Republic capital planet and has luke and Kylo on the run with Han and Leia split between them and Asoka. The entire movie is Thrawn winning, and a constant chase to hunt down Luke. By the time Luke and Kylo gets back to Leia and Asoka, most of the republic has been defeated. Luke and Kylo discover force sensitive people during their flight. Jedi's numbers are growing. Thrawns Siths are also gaining in strength. 2 main siths with death squads of sith under them. It is found out Thrawn is searching for something.
3rd movie - Thrawn has found the former Emperor. His power is all but diminished, Thrawn uses his sith goons to get objects needed to restore the Emperor's power. Luke, Kylo, Asoka, and Bridger find out about the quest and are forced to beat Thrawn to the relics. The emperor succeeds and returns to full strength. He is operating in the shadows until Bridger discovers he is using the space between time to jump to different points in history to make sure his new rise to power will be swift. Bridger and Asoka go into the Space between time to view the damage the emperor is doing.
4th movie - Luke fights the emperor, but Leia dies in the process.
5th movie - Asoka and Bridger take down the death squads, Kylo fights the emperor, Kylo dies.
6th movie - Bridger, Asoka, and Luke fights their way through Thrawn's defenses, gets to the emperor and Luke defeats him through amazing use of the force.