I'm pretty sure if Larry David called up tonight and gave the green light for another season they'd be ready to start filming tomorrow. From all I've heard he's the only one keepingi t from happening.
He was on Howard stern a month or so ago and basically said maybe he'd do another season but was obviously completely non committal. He said he would be fine with it just being over and if he did do another season it would just end like this last one did because after the Seinfeld finale bombed so bad he will never write another finale.