As far as KOTOR III goes, I think the Exile should not be involved in the story. If you think about, the galaxy as a whole does't know what is going on, only that there was a relatively minor skirmish between the Sith and Republic at Telos. Only the Jedi masters and the party members know about the Sith threat throughout KOTOR II. So, in effect, most of the events of KOTOR II go completely unnoticed by the public.
The major theme of the Exile was his ability to turn away from things Revan/Malak could not (war, power, the force, etc.) So, in my opinion, he should leave just as suddenly as he arrived. The effect would be he/she showed up to stop the moster he/she created. As far as the galaxy is concerned, he never came out of exile and the Sith Lords never existed. Mainly, this eliminates an extra character running around KOTOR III without an official name, face, or gender.
It can be argued that the KOTOR *series* has been based on Revan. I think KOTOR III should be about Revan's final fate.
I also think Revan needs to be given an official gender, face, and voice. This would allow for meaningful appearances by him/her.
The storyline of KOTOR III could go something like ...
... Revan discovers the *True Sith* (who we will find out are responsible for the start of the Mandalorian wars) in the unknown parts only to see that they have amassed a massive fleet and are preparing for an attack on the perpetually crippled Republic. This could be shown in some sort of cutscene or playable prologue...
...Meanwhile, the playable character is similar to Anakin in Ep. II - an apprentice based in Coruscant who shows much promise and is just starting to lean lightside/darkside. The PC is sent on missions with his master and finds signs of an impending invasion from an race never before seen in the galaxy... shows much progress and is Knighted in a cool ceremony...
...Revan returns halfway through to unite the Republic under Carth, Mandalorians under Canderous, and rebuilt Jedi Order against the threat (which will finally explain certain parts KOTOR II). Revan takes the PC as a general or lieutenant or something ... and the actions of the PC determines wether Revan defeats the *True Sith* and a) rejoins the Jedi order and becomes part of the council or b) upsurps all power, becomes absolute ruler (similar to Emperor Palpatine). This would mean the cumulative choices througout the game decide the ending, not one big decision towards the end.
Rip away ...
