Yea I also heard that it might be the last one =(
Doesn't sound that way to me:
"Assassin's Creed is all about cycles - we have the Ezio cycle and the Altair cycle, and both of those are set to conclude in Revelations and we have the Desmond cycle, which is set to end on December 2012" <- Suggesting that the only thing ending with the next release is Desmond's cycle.
"Since the first game released in 2007, Assassin's Creed releases have come annually. Amacio added that this schedule will likely slow down after next year's installment." <- Saying that the release schedule will slow down suggests that it it's far from over.
"But there's many cycles within the brand - that's the whole point. History is our playground." <- Clearly suggests that there are more cycles to be laid out than the Altair, Ezio, and Desmond ones.
As for what this one will be about. I'm still sticking with what I started thinking about back when Assassin's Creed 2 released, and it will either happen now or never. This game will be more about Desmond than another past assassin. The new game itself is meant to be centered around whatever is supposed to happen in 2012, and so it wouldn't totally make sense for it to be like the other games where you're in the animus primarily and then toward the end and at other periodic times you play as Desmond. This one will, in all likelihood, have you controlling Desmond more than anyone else. How that will work out is beyond me though. But it just wouldn't make sense to call this game the major Desmond Cycle and make it centered around the 2012 crisis without having it take place mainly in the present.