I'd guess they'd have to attack Google's perceived weaknesses, like privacy concerns. If more people decide they want the sort of thing DuckDuckGo is offering,

I'd guess they'd have to attack Google's perceived weaknesses, like privacy concerns. If more people decide they want the sort of thing DuckDuckGo is offering, then people might switch. And definitely, better filtering. Being able to construct more sophisticated and targeted queries would be useful. A site that did both with sufficient coverage of available websites would be nice.