Tonight, I spent some time looking at the track list for Revelations, and I believe I have a good idea of the chronological order of the plotline.
Ezio Auditore da Firenze
The plot for Ezio Auditore da Firenze begins with him invading Masyaf, as we saw in the E3 preview for the memory, "The Wounded Eagle." In this memory, Ezio heads to Masyaf to acquire one of the Keys of Altaïr from Leandros. During this first attempt, it seems Ezio is captured by the Byzantine Templars, but manages to escape.
From Masyaf, Ezio seems to charter a ship home, and on that ship he briefly meets the young, ambitious ruler, Suleiman I, as well as his later wife, Sofia Sorto. Once in Constantinople, Ezio is greeted by the Master Assassin of the Constantinople Assassins Guild, Yusuf Tazim. The two discuss the state of the city, before performing Leaps of Faith off of the Galata Tower, in the classic introduction scene.
This next area in the plot line appears to involve Ezio having more confrontations with Byzantine Templars, and later assassinating Manuel Palaiologos. Ezio then appears to invade an Ottoman cistern, possibly for a Key of Altaïr. Next, Ezio appears to assassinate another figure, and heads to the Forum of the Ox to acquire yet another Key of Altaïr.
After collecting this Key, it appears Ezio exits the Constantinople harbor by destroying ships using the Greek Fire. Later, Ezio goes underground to the Templar city of Cappadocia, most likely to recover the final key.
The next sequence with Altaïr appears to be of him returning to Masyaf some years later, and killing Al Mualim, and then burning his body. During this sequence, Abbas engages in a heated argument with Altaïr over the body's burning, and shoves him off of a cliff. Abbas then climbs a tower in Masyaf and begins using the Apple. Altaïr would later find Abbas completely brainwashed from the power of the Sixth Apple, and would retrieve it from his mesmerized body.
In his last sequence, it appears that Altaïr regains control of the Brotherhood, and appears to pass the torch and reign of the Order on to his successor.
Well, that's it for this blog, guys, hope you enjoyed this little speculation. I'm sorry if some of this information isn't the most accurate, but please remember it is speculation and just a fun guess at what Revelations has in store for us.