IGN has posted a new articles on AC:R with video I haven't seen elsewhere:
Assassin's Creed Revelations: The Three Heroes
In particular, note the video "Desmond's Mission"
: Desmond meets a guide in the "Black Room", the deep interior of the Animus in which his mind is trapped, who tells him how to repair his sanity. Who else could this be but Subject 16?
I've enjoyed some of the theories about 16, and I favor the theory that the construct we met in AC:B is the mind that the real-world Subject 16 lost. His consciousness and memories got trapped in the Animus, but managed to hold itself together like an artificial intelligence.
Now that we see him, he looks like...no one in particular. But he must have ancestors in common with Desmond if Abstergo was using him. Perhaps we'll see his backstory in a separate game at some point (probably one of the crappy handheld side-stories).
And what's his future in this storyline? Will his mind and body be reunited?