There are very few games that take place in Revolutionary era America (though that can be said for many settings), but with that said, I think it would be a poor decision for an Assassin's Creed game such as III... might be better for spin-off, but colonial America didn't really have a whole lot of large, urban centers (so what are we going to climb). That picture also looks like fan-art, to be honest... converted AC II box art. Also, unless Ubisoft are going to milk this thing even further to death, I would think AC III would feature Desmond as the protagonist, for once and end the series.
What I'd like to see is them to finish up the core series and Desmond's story with III, but then afterwards, in the course of nice two year intervals, release spin-offs without the animus and without Desmond, but all being about differing prominent assassins at differing historical periods just because I think Ubisoft do some really neat stuff with historical twists/conspiracy and urban gameworld design. So, I'd say get III and Desmond's story out of the way in a modern setting, then for the next-gen, introduce some spin-offs with perhaps one taking place during the French Revolution (Paris, je t'aime... et Versailles aussi

), another exploring, if possible with urban limitations, this American Revolution setting, another in Japan, maybe one in Russia, etc. I'm just trying to imagine all these wonderful places fleshed out Ubisoft-style on next-gen console hardware... would be great, in my opinion, and we could ditch this convoluted plot they've extended for cash-grabs long enough. Two years should separate the games, in my opinion... need more time to relieve tedium, allow more to be developed, and essentially provide a fresh feel that makes people actually wants to play, again... like with AC II and it's brand new introduction of Ezio and Renaissance Italy.