I don't know if anyone has posted this yet, but I think that Spa-Francorchamps might be in GT5. It isn't listed on the front page of this thread, but I have compelling evidence to suggest that the track actually might be in GT5!
Here is the evidence:
Taken from this IGN article:
Gamescom: GT5 Course Maker Unveiled
Notice the highlighted Belgian High Fens? That piqued my attention, so I looked on Wikipedia for some info, and here is what I discovered.
This is an image of the Belgian High Fens, If you look, you will notice that to the left is the town of Spa, where the Grand Prix circuit is located. Could this be proof that Spa-Francorchamps is in GT5?
It would certainly ring true with my understand of the track editor - that it allows you to create tracks from existing track locations within the game.
Taken from this Wikipeida article:
High Fens