How I'd bring him back would actually be in the Jedi Fallen Order series, but make Starkiller the protagonist. He starts out as an Inquisitor, he encounters Cal and Cere and kills Cere in the beginning, where you play as Cal in the tutorial section of the game. Then switch over to Starkiller, and play the game as him hunting down Cal and other Jedi like in Force Unleashed. He is an Inquisitor, but he is also still Vader's Apprentice. Being an Inquisitor is how Vader is able to maintain teaching him without alerting Sheev, "or so we think", betrayal, turn to the light all that. We can get Starkiller back, as well as Juno and Kota, maybe bring in some other Jedi characters who are floating around but unknown and all that.
It's sloppy, cheesy and kind meh, but still better than 90% of Star Wars stuff nowadays.