Yeah, they are vulnerable and can ill-afford to spend $10M-$20M (or more) to settle. Don't get me wrong, I am no fan of most securities class-action lawsuits, as they provide a feast for the lawyers and crumbles to the plaintiffs.
I believe that PACB are vulnerable since their own statements can be used against them. For example, about two years ago Hugh Martin said something to the effect of "when we are ready we will enter the $1000 genome competition and just win it". Sure, that was well before the IPO, but try to explain that to a bunch of rednecks in the Eastern Texas Court District. Ditto for the distinction between 99.99% vs. 99.9% consensus accuracy and 80% raw accuracy. This whole situation is a dream for the ambulance chasers and they will not go away unless PACB settles.