Been meaning to get back to this thread. I'll go ahead and type, because I'm probably as ambitious as Kaz in this area.
Give Gran Turismo a third mode of play alongside Arcade and GT Modes: FIA GT PRO.
This would be an encapsulation of the motorsports world, giving you a chance to rise through the ranks like all the race car drivers of history did. I'll propose two ways to begin your career.
One, start rather like GT Mode does with a certain amount of cash to buy a new or used sports car to enter an enthusiast racing and motorcrossing group.
Two, begin with racing carts.
In both of those, you select a region you call home: Asia, Europe and America. This will affect the tracks you'll be racing on and the kinds of vehicles will be slanted towards those regions to an extent. License tests are involved. While some might want to use the License Test results from GT Mode, I think the new physics of a new GT game would make it a justified requirement. The usual bronze, silver and gold levels could be included, with rewards for getting higher levels either in cash and/or sponsor interest. Sponsorship should be a factor in GT Pro like it is in real world racing. A credit based economy, I'll get to in a bit.
Enter, and thus begins a racing season. A "season" consists of a series of races in which you race for points, finishing in a championship which gives more points, for a "wild card" player who isn't doing so well to still garner some standing in the ranks. The season at this level will be rather short, with fewer laps, say three to five laps or so, in five to seven races plush the championship. Bots will have names and racing personalities. You will be allowed to practice, then qualify for racing position. Races should begin with a standing start. The economy if it exists will be to support your car or cart. Damage must be repaired. In the case of car racing, upgrades could possibly be purchased, and sponsorship at this level would mean hefty discounts, especially with good position in the ranks. You also get cool vinyl logo stickers to place on your car. Finish the season with enough points, and proceed to more advanced racing. Optionally, you can re-enter the season as reigning champion and defend your title next season. At any point in the ladder, you can re-enter the season as many times as you want.
The economy would also figure in to moving to the next level, an SCCA-like semi-pro to professional racing group with several ways to go and grow your career. Pay a fee to enter. If you didn't finish well enough in your car or carting season, you could pay a fee to be accepted as a provisional racer. License Test again, with the same potentials as before. Pass, and you select from a few low level options, such as the Miata Cup Series of one make races, or something with some variety in moderately powered race modified sports cars like the Ford Focus, Honda Civic or Nissan 240SX, around 160hp or so. With an economy, you would have to buy the car and hire a mechanic. You get to design a livery for your car. Proceed to racing. The season is a little longer, the races a few more laps, and the challenge is a bit higher. Depending on your performance, the sponsors will provide equipment or even pay you a tidy sum. Finish well enough, and proceed to the next series and season.
These are more competitive with higher powered cars: Ford Mustang, BMW 320i, Honda S2000, Nissan 300ZX and the like. Sponsorship is more lucrative, the liveries more flamboyant, the bots slightly more aggressive. You now have a pit crew. The season is longer, and so are the races: 7 to 10 laps, and 10 races to the championship. You begin racing at night.
Advance to something serious, the world of FIA motorsports. Begin at GT4 level with some more serious racing machines, and work your way up through a few seasons to to GT1, where you'll be racing the likes of Aston Martins, BMWs, Jaguars, Ferraris, Ford GTs and Saleens among others. In Asia, you'll be racing Honda NSXs, Cizeta, Spirras, Supras and the like. You will have more night racing and may have to deal with weather.
Graduate from this into high level motorsports in a wide variety of classes: NASCAR, USCC (formerly American LeMans Seris), WRC rally, FIA Touring Car again, Super GT, a fantasy Asia GT, Australian V8 Supercars, Formula GT and anything Kaz wants to include. Change leagues with a racing test, and have at it... master them all!
Some sort of format like this is what I want to see in GT7. It has plenty of room to be tweaked and massaged, but something like this would keep many of us racing for years, until other games or the next GT lure us away. If Kaz did this though, I'd happily camp out in GT Land unless some amazing racer came along, like another P CARS or a serious Forza. But this would make me right happy.
Edit: one quick addition. I would like an Event Maker to be detailed enough to recreate one of these racing seasons down to the flag marshalls. 100 races would be a little crazy, but it shouldn't be out of the question if you really want that, though 50 plus a championship should be entirely doable. Where to put it though? If something that serious is a bit too simmish for GT Mode, maybe it should be stuck in GT Pro as an option.