I'm torn between March 2010 and June 2010. Maybe the June 2010 response could have been "June 2010 or later." To be cautiously optomistic, I'm going to say March 2010. A different scenario could be that E3 2010 rolls around, and we'll have an almost completely concrete look at GT5. If we don't learn anything more between now and (at least) the Tokyo Game Show, then we'll certainly learn more on this title and what to expect by this time next year. The worst-case scenario (to me) would be this game released in November 2010, maybe after Thanksgiving in preparation for Christmas next year.
But if I had to guess right now, March 2010 is a safe pick. However, I am hellishly unsure March 2010 is even a clear date. Even more so if this game is released before March 2010.