I think GT6 should include every car that was in GT-GT 4 the ended up on the cutting room floor. I miss all of the race modified cars from 1 and 2. Some of the race cars like the 1965 Shelby Daytona coupe and Silhouette R31 Tomika GTR from GT2 would be nice. I mean honestly GT5 had the most GTR's of any GT game but didn't include that one

I also miss the Auto union car from GT4.
As for cars that were never in GT here is a short list,
-All BMW M cars from the M1 to the M6 gran coupe
-BMW E9 CSL "bat mobile" and the E21 320 touring car
-Audi RS2
-All 1930's German grand prix cars
-Movie and TV cars such as the BTTF DeLorean, 1974 Dodge Monaco "bluesmobile", The General Lee, Kitt, Starsky and Hutch Torino, Bullet Mustang and Charger and any others GT fans would want to drive
-Vintage NHRA Drag cars (1960s and 1970s) such as Tommy Ivo's AWD multi-engined Vista Cruiser or Don Garlets Swamp rats
-Vintage NASCAR (1960s and 1970s)
-Vintage F1 and Indy cars (1960s and 1970s)
-Vintage Rally cars (1960s and 1970s)
As for tracks again I would like to see ALL the tracks from the previous titles.
For tracks new to the series,
-NHRA dragways like Pomona and Indy and Vintage dragways like Lions that was in southern California and York US30 an old airport in Pennsylvania that was used for drag racing in the 70s and early 80s
-All Monza layouts throughout history
-All Nurburgring layouts throughout history
-All current and vintage NASCAR tracks including road courses
-All current and vintage F1 tracks
I'm not asking for all of these things but if Kaz would just add a few of these things it would make GT6 great!