I think your ideas above are rather good.
Alright, I really didn't want to get into this yet, as my story isn't totally fleshed out or finished yet. But I'll just tell you guys the basic idea behind my "KOTOR III fantasy story" or whatever you want to call it.
It starts with your selected customized character in the chambers of a Jedi Master. Your young padawan is kneeling before your master, and it being "tested" on knowledge as part of your training. I'm assuming any good Jedi training would require knowledge history and past Jedi related events etc. so your master is asking you a series of questions about the past. He/she asked you about the mandalorian wars, the Jedi Civil Wat, Malek and Revan, The Exile and Telos and the reconstruction of Dantooine, and all that fun stuff. Here is the perfect opportunity to set up all the necessary events from the previous two games. Your answers to your masters questions will determine the outcomes of the previous games, similarly to the Atton Rand meeting in KOTOR II, although this would be much more obvious to new players of the game.
Anyway, the story... During your studies with your master, the Jedi Academy you are attending is attacked. I don't know where the Academy should be. Telos maybe? Not Coruscant though.
In the fight to save the Academy from this mysterious new attacker, your master comes to face the leader of this group, appearantly a Dark Jedi. Maybe a Sith Lord? You run out of your master's quarters drawing sabers with the rest of the students and masters present, trying to seek out your master. But just as they cmoe into view, you witness the final fight between your master and the Dark Jedi. Your master is killed. By now the enemy is beginning to retreat, seamingly having accomplished it's goal, although many of the Academy are spared.
Your shocked padawan is approached by the strange force-user who killed your master, kneeling down to your hight. Almost like a parent would to console a child. The conversation goes something like this:
Dark Jedi: "Do not fear me child. I mean you no harm. I am sorry for what happened to your master, but certain events are unavoidable. Yes, you are indeed a strong one youngling. You will become a great asset in the things to come. Listen closely. You must complete your training here. When you have learned all there is for you here, travel to Coruscant. Your destiny awaits you there. No doubt, things will become much clearer, not just for you, but for all the Jedi counsil, by the time you have left this place. Stay safe child."
The Dark Jedi leaves before the remaining masters at the Academy can reach the padawan. You can feel something very familiar about the mysterious Jedi. Not in a personal way, but the force tells you there is something very familiar about that person. But who is it???
Wait and see.
Maybe I'll post some more later, but this is basically the intro I have in mind for a story. Eventually the PC will complete the training at the Academy, and maybe pick up a party member or two. With no true master guiding you, you leave the Academy when you feel ready. You feel a strange pull. You remember what the stranger said to you and travel to Coruscant. What awaits you there? Do you seek to fulfill your destiny, or do you seek revenge? And who exactly was it that killed your master? There's only one way to find out.