the filesize does seem a bit large for what they mentioned. ther must be some sort of "media" included. Track. Car. More music (would have been mentioned so probably not) or new sound effects (same here).
replacing some code or even adding a new feature that does not require its own new media elements would make it a much smaller update than it was.
My money is on a new track. Motegi seems logical given the clues people have noticed...
And you're probably right. There is the little issue of the cars that will be available in your trailer....that has to have some file size content.
My guess is that they have put the prize cars into the gamedata to coincide with the gold medal accomplishments you have earned so that they will be available at the end of the GT-A Competition.
That there may be a track (or tracks) like Twin Ring Motegi is entirely possible, however, they had Silverstone track competition last year and we did not get that track from the results.
It would be nice to Get Motegi and its variants (that would be 4 tracks in one).
But, one can never speculate with PD...who the :fuck knows what that whacky Kaz will come up with next.