In the aforementioned interview (which you can find here
around 0:55, the interviewer asks the cast and Peter Jackson about their most anticipated scenes in 'The Desolation of Smaug'
Andy Serkis' response is clearly shrouded in mystery - he himself states that he can't reveal much however (and with a smirk forming over his face), he mentioned that "the Lake-town sequences are pretty extraordinary."
It's pretty vague and general as it may include three major sequences that we know of: -The Bard/Master general storyline
-The Legolas/Orc-fighting narrative
-The Destruction of Lake-town
Out of these three, we can eliminate the first one and be quite certain that Andy is primarily referring to a specific action sequence, because as he continues to discuss in the interview, he says that "no matter how big the canvas is ... it's always about the small things" (or something similar).
And whilst we can't be certain of how the other two sequences will play out and who it will involve, I can't help but think that Andy is referring to Smaug's attack on Lake-town.