Title
I'm just curious if this is going to be titled Assassin's Creed 3 or 4. Or if they're going to drop the numbering scheme and just go with a subtitle like Brotherhood.
All indications are that there will be a game called "Assassin's Creed III". Subtitles like Brotherhood are for sequels/prequels to the main, numbered titles.
I hate when people call ACB "Assassin's Creed 3: Brotherhood". It's AC2.5!!! 
But yeah, it'll be AC3.
Before it was given the Brotherhood title, it was referred to as the "Assassin's Creed II: Episodes" project.
So unless they decide to make this into another Brotherhood style sequel, this will most likely be AC3.
I believe they actually have had a team working on this next one since they finished AC2*, so hopefully it isn't as weak or rushed as Brotherhood felt.
*From an interview from either just prior to the release of AC2 or in the months shortly after, Corey May (lead scriptwriter for the series) was asked about the "next Assassin's Creed", he responded you mean AC3 or that Rome thing?"
Brotherhood shocked me with the amount of changes they made and content they added. Most of it wasn't legit Assassination content, but it was a staggering dearth nonetheless. And then Multiplayer!
Granted, I came into Brotherhood with the lowest of expectations, expecting a few extra kill animations and the same style of gameplay as AC2, only less. But it has the best cutscenes of all the AC games, and really great scripted moments. My only wish is that AC3 has the same amount of variety but with NO scripted legit assassinations, like the colleseum one. Scripted events should be for giant battles, like the villa invasion. That was a genuine pleasure to experience. And AC3 should hopefully have more content, since AC2's content lasted quite a bit longer than brotherhood's. And melee combat should be as hard as AC1, but more movement based, with counters that reuqure you to dodge with the left stick and then attack, and getting into a fight with a giant mob of 7 or so guys should be nigh unwinnable. And enemy ranged weapons should drop you almost instantly, thus giving more incentive to taking out rooftop guards and balancing the fact that you have instantkill ranged weapons.
Anyway, yeah, the legit one's gonna be AC3, I doubt it's coming out this year. I think they're planning a generational leap, probably both in the graphics engine and mechanics.
But one more like brotherhood will probably come out this year. Set in a different era or I'm not buying it unless I buy it used, so Ubi gets no money for it.