This reflects a similarly large post I'm noodling on for the overall wishlist thread. Many of you have covered well my wishes for tracks and cars, but these are my two bits.
TRACKS
All the classic fictional Gran Turismo courses they can sic their workstations onto. Red Rock Valley is an old fave of mine, more interesting and engaging than Midfield which is rather vanilla to be frank. I'd also like to see the Circuito de la Sierra, the 17 mile long monster from GT6. Add in a smattering of real world tracks which are appropriate for certain GT appropriate racing leagues.
Another big return I'd love to see is the Course Maker.
CARS
Since Gran Turismo has always been something of a car cyclopedia, and with such a recent focus on motorsports and esports, I'd like to see PD give us a number of race cars from the glory years of racing history, from the 1980s to 2000s period. Also, sports cars which can be race tuned to qualify for them. There are so many wonderful examples from GT / Touring Car and DTM, ALMS, BTCC and WTCC I'd love to see make their return or unveiling in GT7. One key entry I'd love to see is the Ferrari 575 Maranello GT. And Lotus, which I truly miss. There needs to be an Esprit race car in Gran Turismo. And Ginetta, and the Audi Sport Quattro, the Ferrari 355... gosh, there are so many I could go on forever.
To go with these beauties, GT7 needs a whole gob of championship races for them, which shouldn't be that hard to make. Additional custom liveries should be made for them, as well as league badges and number plaques. I'd hope the Ferraris would at least have racing stripes and some decals. They've set the stage for this already with their WTC series. To add to this, I want to see a Gr.5 class added which provides racing with even lower powered modified sports cars in the 180-230hp / 500-ish PP range.
To go along with all this, Race Mod needs to return, because adding racing parts to a sports car just isn't quite the same, or give the same handling.