"South Park," which begins its 12th season in October and has been extended to 15 seasons, is no longer merely the crudely animated, rudely scripted tales of Stan, Kyle, Cartman and Kenny. It is now a studio, a digital hub, a creative powerhouse in its infancy — but with the potential to become the kind of marketing monster that the boys might well find themselves fleeing from, a monster like, say, Mecha-Streisand.