I've been reading the Book of Sith, and I've formed a theory that Revan is both the Chosen One and the Sith'ari. To make things easier, I'll just list the evidence for his fulfilment of each prophecy individually:
Evidence for him being the Chosen One:
- The Chosen One is said to be extremely powerful in the Force, which Revan quite clearly is
- The Chosen One is said to bring balance to the Force, and Revan is one of the few completely balanced Force-users in history:
He's trained with both Jedi and Sith
He's fought for both Jedi and Sith
He's fought against both Jedi and Sith
He's left both Jedi and Sith
- The prophecy also makes reference to a place called Mortis, of "impossible geography" with a "gargantuan monolith" and gods of dark, light and balance, which to me sounds like Malachor V (with the monolith being the Trayus Core) - assuming that Revan is the Chosen One, that makes Malak dark and the Exile light. Alternatively, I have a different interpretation that has the Exile still as light, but Kreia as balance and Sion as dark.
Evidence for Revan being Sith'ari:
- The Sith'ari is free of all restriction, and Revan has no absolute loyalty to anyone save the people of the Galaxy, and acts purely on what he believes is right
- The Sith'ari will lead the Sith and destroy them, both of which he did in the Jedi Civil War
- The Sith'ari will raise the Sith from death and make them stronger than before - Revan ordered the creation of the Mass Shadow Generator, which was responsible for the creation of the Sith Triumvirate, two of which were raised from death, one of which is infinitely powerful.