Well, we can learn more of the true sith, but if they become the main problem in the next installment then .... no one will be able to stop them because:
1. The republic has just barely began stablizing after the Jedi Civil War
2. There's rarely any Jedi left
3. The Old Masters of the Force would make the Jedi/Sith of today look like children playing with toys ( and I doubt the True Sith would allow their skills with the lightsaber to diminish so easily )
Revan, no matter how powerful he/she is, is no match for the True Sith for he's/she's been trained by these "children". Also, Revan left to find the true battle that's being fought elsewhere. If the True Sith is the enemy, who will be the ally? Or vice versa - Sith being the ally and a unknown enemy is found ( but then again, when has the Sith never been the embodiment of the Dark Side ). One side is known to us, but what's the other side? For what's the war when there's only one side? ( easy answer to that
)
In truth, I'm just wondering what'd be the problem if it's the True Sith? - who's going to stop em? Cause the Republic is severly weaken, Revan isn't adequently trained enough, and barely is any Jedi are left after the second installment. Maybe there's also True Jedi? And what of the Grey Jedi - hardly anything is mentioned of them. Then again, was it ever disclosed that the exile went in search to join Revan? Or whatever the exile really chose to do after the encounter with Kreia on Malachor V ( sorry if I spelt that wrong ).
Many uncertainies lie - but we must wait to see what they'll choose to do...
Revan - Life of the Force
Exile - Death of the Force
True Sith - Thought to be hidden in the depts of Unknown Space
Republic - Broken but rebuilding - slowly
Jedi Order - Almost (if not) entirely wiped out
Sith Empire - Unknown to what their status is - (other Sith Lords could still exist)
Whatever the case - the ending should end in a way that would eventually lead to the events in Episode 1 - The Phantom Menace
-- Disregard my reply if you disagree with what I say --
-- No one ever said you'd have to listen to me --
-- Believe what you wish, with the way they ended that one, the possibilities are enless --
-- I just want to know whether Revan and the exile are male or female ^_^ --