I wouldn't go that far, at least with GT7. But during the PS3 era? If you placed a high bet that PoDi was aiming to develop the Gran Turismo game of many players' dreams at the time? You'd win that bet for sure.
The biggest supplementing evidence for this case is found in the latest prototype of GT5 that was discovered, "GT5 Demo 2010". The database files contain registered entries for every single vehicle that was featured in Gran Turismo 4 and the PSP spinoff title, even the likes of the 1915 Ford Model T and FPV were set to feature again. Not only that, but there's code sprinkled everywhere throughout the prototype that suggests the inclusion of "Standard" courses. All of the GT4/PSP courses are actually completely registered in the databases, just that the files are missing from the actual prototype itself. It would appear that the course files themselves found in GT5 were actually updated for the release-to-manufacturing build of the game; all of the GT4/PSP courses that work on the final game have had their files updated to do so, so the concept of Standard courses being a part of the final game might have been closer to a reality than one previously thought! But unfortunately, wasn't...
Another individual (who chooses not to be named) found out that why the particular courses that are listed as not-working on the Course Database over at The Cutting Room Floor is because their files have not been properly updated to work with the release-to-manufacturing build of the game and beyond. Previously shown off in the Discord server are screenshots of these non-functional courses working 100% as intended...if they are backported to GT5 Demo 2010. As all of these courses are registered into the databases of that build, it's as simple as adding the files to the courses and then enabling them for selection in Arcade Mode.
Whenever I find the time to setup my PS3 again, I'll post these screenshots that I have saved.
The original PoDi plan for Gran Turismo 5 was indeed a game with all content from previous GT games, both cars and tracks.
This plan was already told by Kazunori Yamauchi when he announced Gran Turismo HD divided in two games:
-GT HD Classic - Only classic content, with some improvements like 16cars and also bikes. You needed to buy cars and tracks with real money (it would cost more than 600€)
-GT HD Premium - New content , new improved graphics, new game engine build entirely on ps3.
The idea was "scraped" in favor of a free demo , Gran Turismo HD Concept , and the announcement of Gran Turismo 5 Prologue.
I wrote scraped in quotation marks because they never abandoned this idea; Gran Turismo 5 features infact almost all cars from GT4, and many of the previous tracks. You can notice that few tracks got some major improvement ( like high speed ring ) while others looks almost identical to their GT4 counterpart with just improved textures and few extras (like trial mountain). The rest of the "untouched" tracks would have been the standard tracks, those 2gb's of unused circuits.
By digging inside the GT5 2010 Demo, there are menu pictures for all tracks, including also GT5's unused ones. The interesting thing is that many of the tracks that would've appear in GT5 use their ps2 version on those screenshots. Here's an example:
This is Cote D'Azur menu screenshot: GT5 top, GT5 2010 Demo bottom. It could be possible that they used ps2 version as a placeholder, before making the shot on the ps3 version, or it was going to be a Standard Track (considering that there's montecarlo_ps2).
At the end they were probably too ambitious so they decided to cut off the idea, complete polishing some of the tracks and remove that idea... by hiding the files into the game
