I think kotor 3 should put an end to trilogy (good old star wars tradition) so you should get the chance to fight and defeat the true sith.
I liked the idea of starting on coruscant, it would be great to see and walk that planet.
I would start the game by setting the apperance of revan and the exile (face, gender, jedi class) so that they could look the way you wanted them in the first two games (i know this would ruin the suprise when they show up, cause you know they're coming) it would be fun if you could those your main character to be an alien and customize your lightsaber as wel (color and hilt like in jedi knight)
Once the game is started you begin as a padawan on coruscant receiving his final mission to prove his worth before becoming a jedi knight. This mission could come from the new jedi council (including the discipel, bastila, handmaiden -as librarian)
On this mission you ran across some kind of new creepy sith. You hurry back to the council telling them about this new threat. They make you jedi knight and you get your own padawan. Then you 're off to find someone who could know more about these sith.
You could encouter some old friends (like jolee, really my favorite) and new ones.
Finally the true sith strike and you have to hurry to save the republic (again) first by finding the exile and revan and together lead the republic and jedi to war against the true sith.
I don't know much about rpg's (only played kotor) so i don't quite understand what you're all are saying about those other games but i liked the idea of not being restricted to the guardian/sentinel/consular thing, you'd have to customize you're own character to your liking.
My final suggestion is that you should be able to play with multiple parties, not like in kotor 2 but three completely different ones: one for yourself and one for revan and the exile each once you find they. You should lead each of these to the final battle, each searching for support a way to stop the sith
Once they're defeated you could see a state-of-the-art cinegraphic showing two of the sith fleeing the destruction of their power and allready planning to seize power again
i know, this is a lightside scenario, should think about a dark side one to
