I've always thought that they should incorporate a basic time frame or schedule into the game.
When you start Simulation/Career mode off, they should ask you for the month, day, and current time. Basically what I'm proposing is that they give you a real life calendar in the game.
Then the game can have listed what events are being held each day for that whole year. An actual, real life year. Some events would be held one day, and others on another day. Maybe we would even have some one time only events with a special prize car. If you miss that event, too bad.
I think it would make the game feel more life like to have a real racing schedule. You would basically have to decide which events you want to participate in each day to win certain trophy's and prize cars. Some days would have few events, so you could attempt them all, and others would have many races on one day and you would have to decide which one's you would want to race in since attempting them all would not pe possible in the allotted time.
Concerning prize vehicles, they should only have one prize car available for an event on one day. Then if that event was held another time in the distant future, there would be a different prize car available, not the same.
This would help to attain more variety in the game. And, include tough decisions that could either make you or break you in your racing career.
Considering that this is going to be an on-line game, I think variety is necessary so we can have more entertaining races. On-line mode would have to have different classes though. Based on several other factors to allow all the cars entering a chance at victory.
You see, the problem I had with the other three predecessors is that you could obtain too many cars, and win too many races way too quickly. For me, that killed the fun after time, and made the slower and less capable cars from the beginning of the game obsolete.
Coming along with the calendar, would also be better implementation of weather elements. Based on the time of day, it could be light out, or dark out. Some endurance races could even continue on into the night.
The time of year could also depict the type of weather we would encounter. Spring and Summer could bring large rain storms and/or long droughts. Both affecting the cars depending on how Polyphony Digital decides to deal with vehicle physics, and damage.
Fall and Winter could bring cold days where the cars performed sluggishly until they warmed up, or snow storms that could cancel race track events and/or provide extra challenges for rally racers performing on that day.
One of the problemswith this concept, unfortunately, is the duration of time. Many people would rather not wait half a year for a certain event to come. Though this could be balanced out in two separate ways.
One, is that the time system could be made into various ratios. For example one year could equal half a year; One day turning into twelve hours. And in this shortened amount of time, there would be much more activity. But less you could participate in since you would not have as much time to work with. There could be many different possibilities. Which is why you would most likely be allowed to be able to set up your own ratios based on how much and how often you play the game. Though this is if the concept was offered off-line only.
The second method isn't necessarily a change, but a different take on this idea. Think about it. Everyday there would be new races and new cars to win. You would have to work hard to be in time for the event you wanted to race in. You would have to also watch how long it takes you to finish a race. If you took longer than usual, you might be late for an event being held right after the one you were currently in. This could help improve racers skills so they can become more efficient and acheive faster lap times. Or maybe you wouldn't race again at all again that day. Assuming that they include many more tuning options, and an open race track at all times, you could go and prepare your car for an event later that day, or the next day, or for whatever you wanted.
Now if this concept was available and/or mandatory on-line, then the ratios could not be used since everyone would be running on the same schedule. And the events being held throughout the year would have to be predetermined and not random. That way everyone would be on the same page.
There is another important factor. Obviously we could not have thousands of people participating in the same event. What to do about this is tricky. There could be a first come, first race basis. There could even be a registration form you could send out in advanced to the system, allowing you access to the race over those who did not register. Overall though, the number of people allowed to race would have to be bumped up to at least twenty-five if any success with this system is in reach. This could provide greater enjoyment for racers. The more action, the better. the more competition, the more racing enthusiasts hooked.
Now comes the tough part. What car would we start out with? Would there be a small selection of cars to choose from with your beginning amount of credits? Assuming that we all start out with the standard 20,000 credits, everyone would have a good chance at victory from the beginning since we would all have to buy low end cars. Or would we be given a car to start out with? And if so, which?
Would we still have car dealers to buy from? Or would we all rely on our beginning car and have to fight for the prize cars from the different events? If so, all the cars you could buy from dealers, would be filtered in the prize car system. If there are in fact over five-hundred cars in the game, then there would be a vast array of cars to win. But after time, seeing as how there would be more than just one event most days, we would run out of new and different cars. Would we need more prize cars? And would we have those existing cars intricately filtered back into the system so others could win them too? I'm certain there are many other questionable items. Though that doesn't mean they can not be worked out.
With the calendar concept, I feel the game itself would become much more realistic. The variety of cars different people would have would make things much more interesting. The way you would have to work hard in order to accomplish races and progress, is much better in my opinion, than sitting for hours on end racing all of the races until they're all gone like in the previous games.
In short, this concept would be excruciatingly tough to execute, but it would be well worth it. You would be able to see a multitude of different races going on at different places at different times. Thousands, maybe even millions of racers, racing head to head in different tracks, races, classes, cars, and maybe even more. And only one person can win the prize car of that one particular race. Imagine the competition going on. Imagine the experience amateur racers could pick up and acheive. That, would be the pinnacle to success for Gran Turismo.
In addition to all of your ideas, Gran Turismo would be in a class of it's own. Forever strong.
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What you do when you find a big a** parking lot with snow on it 
Running on 15" 205's doesn't really give the needed grip in snow 
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