I think Revan could well be a DSer (again?) by the end of K3, twisted and corrupted by his dealing with the True Sith (seeing as what they left at Malachor is what corrupted him--or at the very least put a man, hungry for knowledge and power beyond what he was being granted by the Jedi framework, over the edge--in the first place). But I'm not sure that if such were to occur that he would be a candidate for the role of "Darth Traya." He is/was Darth Revan, and his life is as much about the power he wields and how his choices affect those around him as anything else.
It is my belief that the role of "Darth Traya" more specifically is in reference to a sense of betrayal of the Force itself, or at the very least it's philosophical foundations as stated by he Jedi Order. That is, the fall of "Darth Traya" is in relation to the loss of faith in the Jedi's way of interpreting the Force. That applies to Kreia's decision to follow in Revan's footsteps by giving in to Malachor, spawned by the fact that all her apprentices chose to follow Revan to war (and presumably fall to the DS) against the greater "wisdom" of the Jedi Council, who cast her out because of her abberant teachings. Likewise, Atris felt betrayed by the Jedi interpretation of the Force because in her heart she believed the Exile--who she either admired or loved--was right to go to war. And shame at that belief is what drove her anger and lust for punishment. Surrounded by corruptive Sith holocrons, her faith in the Jedi view of the Force likely eroded even more.
On top of all that, we have the fact that Kreia was jaded by betrayals to the point that she came to hate the Force for controlling her destiny. While that is her belief, it is in no way certain that she was correct about there always having to be a "Darth Traya." Her own interpretation of existence is not the end all and be all, and as someone who was haunted by what others told her were her failures, she could be construed as desperate to justify why she was right. That, arguably, is her purpose behind training the Exile in the first place.
If there is a Darth Traya going forward, the best candidate IMO would have been a *light side* Exile--since I do believe that what Zez kai-el, Vrook, and Kavar tried to do at Dantooine constitutes a betrayal in terms of what the Jedi's interpretation of the Force *is*. The deeds of a LS Exile showed that the Jedi Order, by proxy, would not look beyond the Exile's wound to try to come to a greater understanding of her and the Force itself. That, to me, is a betrayal of "universal good" by the entire system of beliefs the Jedi Order was built upon. I know that my first time playing the game I was crushed by that scene, after all the good I had done and hoped to do by destroying the Sith, and I certainly think that it carries the emotional impact of a betrayal that could lead to a fall.