Are Lambic beers the product of quorum sensing?
Almost certainly not. Species occupy different niches due to their differing growth rates and tolerances. Interspecies quorum sensing and the symbiotic relationship that implies do exist(see: lichen), but open-air inoculation is unlikely to produce them.

Why would the Brettanomyces simply kill time waiting for 'their turn'? It's likely they don't grow as fast as S. cervisiae or other early fermenters, and as a result they're outcompeted until alcohol content rises enough to slow or stop other species. Brettanomyces isn't 'waiting', they're eating and growing as fast as they possibly can. 

Many microorganisms form spores or simply hibernate until conditions are favorable for growth. For highly acid and alcohol-tolerant species, perhaps they sporulate until the mix is acidic enough to guarantee them habitat. This is a form of quorum sensing, but the transmission medium is pH and alcohol concentration.