Lots of great ideas there, I love the one in previous pages about having a better visualisation/organization of the garage (group cars you like, being able to inspect them, view inside, etc...).
I'm late to the party but I'll share mine too
these are small things but quite simple to implement I guess :
1 - Better replay options (or replay editor ?)
I'm not fan of replays in GT sport, most camera angles are good to contemplate cars, but not to enjoy the action on track (like some stuck-to-the-ground cams, etc...). Classic/Dynamic option in GTS is not enough, I would love at least an option that provide really wide picture of action and doesn't miss the critical points on a track where you generally overtake. A replay editor (choosing cams depending on the timeline) would be a killer feature... Or maybe a "simple" version where you press a button during replay to say "hey, I want to see this bit with more angles", and the game automatically gives you the same 20 seconds around this point, like 4 or 5 times, with different cameras angles.
2 - Fix pagination when browsing liveries
When you search for liveries with filters in GTS, you can have tons of blank pages, or pages with 1 or 2 results. Pagination should be applied after filtering
3 - A longer daily "race D" ?
I feel that racing etiquette is better when things are not rushed in a 3 lap race, it would be cool to have a longer "race-D" event in future sport mode (or online), with like 20-30 laps. Well of course you can set up lobbies as you like, but it would be nice to have this kind of event set in the future "sport mode" if it exists
4 - A real podium
Instead of seeing your avatar & car, have a "real" result podium on online races, where you can see the three first racers, with their helmets/suits, and maybe their car, and maybe the national anthem of their countries... would be great for ambiance