I get that NISMO has an up-spec race-spec, but I would like to see it get a bit of a 432 vibe.
Something both upgraded to the top of the line, but also distilled to something more elemental, and a bit more of a collector's item, perhaps more limited edition than regular production.
Sports/race seats, ok.. if they are still good and comfortable for longer drives, and not too antithetical to using the car as a driver/touring car.
A bit more power with more effective cooling... that is fine, just as a bit more optimization... such as a lighter flywheel and more precise balance, with slightly upgraded turbos with ceramic bearings for faster response... sort of the enthusiast/gearhead spec.
Forged wheels with 2-piece brake discs to lighten the unsprung and rotational weight would be very good.
Electronically active or magneto-rheological dampers, an e-gear differential... a bit more suspension and traction tech, if it is both effective and reliable, would be interesting...
Maybe also a case to be made for a valved sport exhaust system, like many other cars are getting lately.
Lightweight bodywork would be welcomed, as long as it isn't ultra fragile or too expensive to repair or replace, because this would be the car to keep, and repair if ever damaged... and shoudn't have to be a garage queen in order to last.
A mild aero-kit perhaps, but not all slats, spoilers, and ducts to try to show off as a factory race car... if it looks more boy-racer ridiculous than standard, and not a clean design... that hurts the special edition/collectability aspect, and one may as well just get the ST package, and modify it with the things I mentioned above.
If the car starts at 35K... this should be doable with a profit margin, for 20 grand or less... putting the MSRP at 55K or less, which S30R32 mentioned. That would take the top of the line Z35 right into Supra 3.0's base price.
Keep in mind this is not retail price modification, where you take off parts that were purchased as part of the car, and put on retail price parts aftermarket. This is baked into the car from the production and supplier level. the retail markup is the MSRP or invoice price. You don't put on base wheels to replace them with forged ones... the forged ones go on in the first place.