VideoGamer, series creator Kazunori Yamauchi said damage modeling is coming to GT5: Prologue. "We're not really planning for a trial or test version," he said, "we're going at it full speed. We'll see what happens." In a separate interview with IGN, Yamauchi expressed hope for a Fall release of the update.
Yamauchi also hinted that weather effects would be in the final, non-Prologue Gran Turismo 5, due out about a year from now. We're not expecting Burnout-esque pile ups, but a fender bender in the rain would be nice.
[Via PS3 Fanboy]