My suggestion for KotOR 3 would be as follows.
First, more of everything. Bigger worlds to explore. More NPCs. More party members. The ability to not be a jedi as a main character. Make the ability to beat the game multple ways like in fallout, where you could be the charismatic leader and **** your way through the universe getting other people to do things for you. Maybe have charisma effect the number of party members. More races to play as.
Longer play time would be cool. Say 40 hours to beat the game just doing story based events, and 70ish hours to complete everything. I cant speak for everyone , but i don't like creating a character playing it then only having 25-30 hours of play time with it. More customization is always a plus. I liked comparing characters with my friends, Fallout 2 characters.
Release the toolset with KotOR 3 like the toolset was released with Never Winter Nights so the mod community can get a hold of it easily and mod the crap out of it. Create more content, keeps the game alive and people wanting more.
Perhaps even some kind of fort on some planet you can customize and build upon, gather forces at. If your sith it could be a sith training academy.
I say drop Revan and the Exile. Create a new story. Something new. Something that does not feel like the movies. To me both games felt like i was playing the movies but with different characters. From a design perspective it is probably easier to not have to worry about all the back story on 2 games to make a 3rd game fit into the story they wrote years ago.
Perhaps for the story come at it from a third angle. Instead of having the jedi and sith fighting and you pick a side, you are say a Bounty Hunter or errand boy from some barren planet in the middle of no where, and your just trying to live through the jedi/sith war. Through that conflict you could pick good or evil, or perhaps some neutral side to stop the.
Or another story angle could be that your senator father was killed and your tring to find out why, and mystery ensues. Let story be not on such a grand scale that you dictate the future of the entire galaxy.
Those are just my humble suggestions. Thanks for the games Obsidian. Cant wait to update my mod to NWN 2, (or to finish my group mod for NWN).
Eric Ic Foster