Anyone feel like making a list of the 70 most likely tracks?
Sure, using Kazunori's explanation from TGS 2009:
"There's 20 locations and there's going to be 70 different types of courses that are going to be in those locations."
1. Circuit de la Sarthe I (chicanes)
2. Circuit de la Sarthe II (no chicanes)
3. Fuji Speedway 90's
4. Fuji Speedway 80's
5. Fuji Speedway 2005
6. Fuji Speedway 2005 GT
7. Infineon Raceway - Sports Car Course
8. Infineon Raceway - Stock Car Course
9. Laguna Seca Raceway
10. Nurburgring Nordschleife
11. Suzuka Circuit
12. Suzuka Circuit East Course
13. Suzuka Circuit West Course
14. Twin Ring Motegi - Road Course
15. Twin Ring Motegi - East Short Course
16. Twin Ring Motegi - West Short Course
17. Twin Ring Motegi - Super Speedway
18. Tsukuba Circuit
19. Apricot Hill Raceway
20. Autumn Ring
21. Autumn_Ring_Mini
22. Deep Forest Raceway
23. El Capitan
24. Grand Valley East Section
25. Grand Valley Speedway
26. High-speed Ring
27. Midfield Raceway
28. Trial Mountain Circuit
29. Grindlewald
30. Red Rock Valley Speedway
31. Citta di Aria
32. Clubman Stage Route 5
33. Costa di Amalfi
34. CĂ´te d'Azur
35. George V Paris
36. Hong Kong
37. New York
38. Opera Paris
39. Seattle Circuit
40. Seoul Central
41. Tokyo Route 246
42. Special Stage Route 5
43. Rome
44. Madrid
45. Test Course
46. Beginner's Course
47. Motorland
48. Cathedral Rocks Trail I
50. Cathedral Rocks Trail II
51. Chamonix
52. Grand Canyon
53. Ice Arena
54. Swiss Alps
55. Tahiti Maze
56. Silverstone
57. Monza
58. Eiger Norwand
59. Indianapolis Motor Speedway
60. Indianapolis GP Circuit
61. Daytona International Speedway
62. Top Gear Test Track
63. Top Gear Drag Strip
64. Daytona International Superspeedway Road Course
65. London Street Circuit
66. Las Vegas Dragstrip
Now, there's about 4 left. I don't want to guess, but it won't be hard to fill in a few more. Perhaps a few more variations? It seems clear, though, that we'll get most, if not all of GT4's tracks + new ones.