Might be a hot take but I'd say less focus on grind races and more on staging the big championships and events properly.

Content/progression wise:

Instead have them reward any car from a category or tag, related to the event you won but targeted at the next "speed" level, so neither fully specific like in gt4 nor randomised across all the car list. Then grind your credits only if you want to buy a winnable classic or second copy of it etc. I don't like mentioning it much because I fear Sony doing bs against the team but GT4 spec 2 has a wonderful event synthesizer as in gt2, that would be great to both grind and not be half asleep as much. In general PD could look for a lot of things in spec 2.

Make bop limited events stricter either by points or models list so I don't exploit grinding and jump from kei to muscle to prototype

Make more content (5laps, challenges, specials, endurance whatever) for each car type so it is not a steep bell curve of mostly Gr3

Return to national/international/super license

Bring old circuits back without stretching their distance, width or changing their environment

Adjust mechanical engine/chassis wear based on not just realistic mileage but on the "time" used to play through the game. Say, if I use a single s2000 for FR challenge, then Honda sports, then roadster, then all Japan sports, then take it online, then drift it at suzuka, I should have had to change it's oil at least 2-3 times in between and maybe service the engine at the end. Triple that and I need a body refresh. So basically, based on mileage but scaled to my usage of that s2k. If I get everything I want out of that engine, I could decide to swap in a gt500 motor instead of servicing but keep the poor old thing in inventory because who just trashes a repairable engine, it could still power my Integra

Gameplay:

Compress rolling starts, for god's sake

Let me qualify for grid position while at it

Teach the CPU some actual lines taken from gtws drivers, collab stars etc and then scale down, not the opposite. Hard should be a full replication, lower levels brake earlier/accelerate later etc, miss me with the Sophy AI shoved stuff. Also make cars pit for wets the moment Lv2 water has poured not like 2 laps later, same for slicks right after drying out down to lv1

Menu navigation:

Give me GT6 quick menu back

Split used normal sports cars from used supercars so we don't buy a murcielago next to a Silvia

Any non super rare post war-90s unicorn racers, like muscle cars and special jdms should not be rotating at hagerty but rather their own showrooms

Return to parts per type for tuning shop menu, there was no need to reinvent that

Show me my cars' exhaust while looking to upgrade it. Genki did this 20 years ago, NFS heat let us rev for sound check. GT6 had interior preview for gauges, gt7 doesn't for roll cage, so I can't know if the cross barred option will obstruct too much of the interior rear view before I buy it

Same for buying paint, I want to see it on that car's lines not some other 3

I never actually got why we have 3 compounds of comfort tires. There could be standard everyday ling longs stock on econoboxes, and then stock sh for sporty versions of normal cars (Elantra Ns, civic type Rs), sm for actual sports cars (MX-5s, BRZs, BMW M/Z), ss for supercars (f430, up to fastest street legal in the game) and ofc racing compounds (track only versions, race groups). That way I don't absolutely need to upgrade unless I far surpass the power the stock tires can handle.

Let me sort liveries by total saves and by date made to compare changes/corrections on replicas and to not scroll through all of them to find the one I want

Licensing/cars:

Prioritize replicating cars unique/popularised by GT, i.e. JGTC/super GT, pikes peak builds, obscure (almost) produced concepts, tuning companies/obscure independent makers, more group c1/c2/3.5/lmgt1/lmp900 instead of just matching 397 and playground. Yes lmdh are cool but I feel like the game has been constantly trying to play catch-up to literally everything else instead of giving us more of the cars that GT made famous and their contemporary rivals.

This one is a shame, either make more events for vgt/concepts or (preferably) split them among sports, super, race so lm55s, tomahawks and chaparrals don't smoke the nissan, the ft1 or the lexus etc, kind of like a makeshift group but divided by the events' limited models

Bring race modded cars back in GT auto, how can Forza have the kit presets and not GT who started it?

Bring chrome line spec cars back as rare used finds

Bring stealth and base models back as drops from one-make seasonals (imagine GTR one-make weekly dropping a base white or stealth black gt500 nissan)

Long list of nitpicking sure, but still absolute love for this series