Ok, after some research around the internetz (from various different sources). It appears that Yamauchi will be giving an official release date "very soon". Rumour has it that this could be at the Tokyo Game Show which takes place September 24th - 27th (GT5 will be released with the GO on October 1st), which would suggest that the September release date is not going to happen. It's been said that PD may now be hoping for a December release, however this could be extended again, but they have promised it will be with us no later than the end of the Fiscal year which is the end of March.
Although no official car/track list has yet been comfirmed, we should expect somewhere between 340 & 700 cars/models, and 50 tracks (including the TG test track, where apparently you can challenge the Stig's Lap Times). The car list will continue to grow after release (though DLC and Updates), which "could" take the list up to 10,000 (if you believe that), from all manufacturers EXCEPT Porsche and Lamborghini.
The only other things I could find are the things we already no about, such as crash damage being included, WRC and NASCAR involvment etc.
Personally, I just wish they'd hurry the f**k up... IMO the problem could be designing the crash damage, it was the one thing they never really wanted, but EVERYONE else did... although I could very wrong. But atleast where getting a full new game, not the "HD update" it was originally supposed to be. All this secretivness is doing my bloody head in tbh... it would be nice to just have SOMETHING to go off!!