Their take on A-Spec and Online has the most room for improvement. No one doubts PD's technical abilities. That has not been where the stagnation has taken place. You have the same exact events in GT6 as you did in GT1. That is sad and unfortunate. If you are so inclined, you can dig up a post I made after nibbles or whatever the hell his name is, was determined that GT couldn't possibly be improved and my inability to draft a design document detailing my master vision of GT at the drop of a hat, proved his point. He then proceeded to harass me about 10 times a minute for an hour until I gave in and had the time to post some musings on possible GT7 "improvements" of a direction GT could go in that would help continue their underlying theme of 'celebrating the automobile'. I wouldn't bother but the TL;DR of it is they really should play to their strengths of car ownership and the persistent state of your cars across your career and online. Own each dent, race a car until it dies, etc. There is so much more to what makes 'your' car unique than gaudy liveries and rims. I know my real life cars dents and scratches like the back of my hand. It would be cool if you knew no one else had the exact same car(s) as you in a GT game. Maybe you shifted your Viper like a dumbass the first 12 races and you blew the stock engine early. From then on, that car will never have the stock engine block, making those with an all stock Viper with 85K miles on it be something of note. I don't know, just my thoughts. This all occurred to me the day I won my first two NGRL races back to back in my beloved Ferrari 512B. I wanted to "frame" that fucking car and treat it like a trophy. It has a history with me, but in terms of GT5, it is just another check box in my garage of 1400 some odd cars.
Persistence is something I believe we will see expanded in GT7, we don't know much about how it will work in GT6, but in GT5 they gave the first steps for an useful mechanical damage, and now they are making (at least) the visual damage persistent.
We already had oil, dirt and body structure (not perfectly but) set.
As for an [online] car ecosystem, unified market/rare cars (original parts means something, limited number of certain cars available), that would certainly be awesome. Maybe when Kaz manages to get his GT City/World plan in production.
Now as for their game structure: I hold the opinion that having you go through all classes of cars is important, from lightweights to F1.
Their system isn't so strict in terms of "evolution" in the middle, but it is a point to point structure. And I don't think it is bad, even if they have the same names from GT1.
The main problem I see is
the lack of challenge. It bores the "used to it" fanbase to death.
And I'd say that even with
artificial challenges (AI still needs improvement, B-Spec racers are
perceptually more daring, knowledgeable), it wouldn't amount to much if retaining the same structure. BUT:
They had this "beginner, amateur, professional" ranks, but they were merely boxes for the events. They could change it to a player questionnaire.
Where if you answered beginner, you'd walk through all the small clubs and events, knowing cars.
Amateur would jump you right into those series of 5-7 races, with harder limitations (in terms of car build and racing assists), against racers that seem to not be racing the tracks for the first time.
And at the far top, you can have professional events/leagues (even races in generated tracks) that require compact cars, germans, and what not. Reach the glory in that category, 10-12 races of 30 laps in a Golf.
They do it with the formula car (most consider it torture), why not with all. Have persistent pilots in all structures since they are named now.
All things that Polyphony has set in a manner and wouldn't be a huge departure, since it is clear they do not want that.
I had a great time doing the first(?) expert challenge set with the Subaru in Laguna without looking in the internet how to tune it. And that was with the opponents always being in the same position at any given time. It would be perfect to have such challenges in an recurrent manner, with plasticity on the races. Getting into a german production cars league, with a hard limit on what you could do, having to tune your car for best performance on each track and knowing the other racers would be driving hard.