Something interesting to take a look at:
https://www.gtplanet.net/forum/threads/gran-turismo-6-career-races-list.291309/page-9#post-9720732
Career structure in GT6 is kind of random imo. If you look at PP restrictions of events you'll notice that they go back and forth instead of gradually going up. The way car classes are organized is weird, there's a kart event in the middle of a group of road car events, then a random offroad event, then a road car event in the middle of the race car events, all of that seems odd and disorganized. For future games PD needs to include more events, more races per event, events for every car class, and group events of similar car classes.
I don't mind future games having the traditional GT career but I think it would be a great idea to have alternate ways to play career. Examples:
-Traditional GT career - player starts at the bottom and has to win races & pass license tests to unlock the next career section and work their way up.
-Custom career - career events divided by class: road car, touring/GT, prototype, open-wheel, rally. Player can focus on a certain discipline or play multiple disciplines.
-Freelance career - all career events are unlocked from the start, players can play whatever events they want in any order they want.
All career paths would have adjustable race length with payouts being adjusted accordingly, as well as bonus credits for disabling aids, enabling damage, and increasing AI difficulty.
Better restrictions would be good too, road car events should not allow race cars and vice-versa. GT3 events should only allow GT3 cars, same applies to other racing class events. Also all AI opponents should use cars that are competitive and are as close to the performance limit of the event as possible.
In addition to multiple career paths it would be great to have all cars & tracks available from the start in arcade mode, along with all options needed to setup custom races offline.