Polyphony boss Kaz Yamauchi has announced that an update to GT5, called Spec 2.0, will be out in the third week of October, with DLC due a week later. Sadly, no word on what's actually in them.
Well, it looks like GT6 won't be out for another 8-10 years at the pace they're doing updates for GT5, unless they're working in parallel on both titles. Unless 2.0 updates standard cars to look less shitty, and adds a whole lot of new content (tracks, newly released cars, new events etc.) then I think they should really start working on GT6.