Considering that all of the courses in Gran Turismo Sport have pre-baked lighting, I doubt we will see a Course Maker feature return anytime soon. Either lighting would have to be done in real-time and possibly contrast rather poorly to the other courses in the game, or lighting would have to be calculated and baked on-the-spot after the creation of the course on the console itself (or sent to a server for processing), which isn't currently feasible for either option. Considering how long it takes the developers to bake in lighting into a course, having to do so for thousands of uniquely generated courses and figuring out proper algorithms for such- it isn't really doable at this time.
I'd love to see the feature return, though, as I enjoyed it in both
Gran Turismo 5, despite players' criticisms, and
Gran Turismo 6. I did enjoy GT5's sheer randomness of the courses that would get generated; you could generate crazy ones that have unorthodox driving lines, extremely sharp corners, or absurd elevation changes where going full-speed would launch you into the air and into the barrier if you weren't careful; the variety of layouts was also better. I also enjoyed the feature in GT6, despite its shortcomings and taking
nearly two years to release even since it was printed on the back of the game's case upon release.
A few members here developed some tools that allowed you to create some truly unique courses, even some old favorites:
I would like to suggest that if the feature would be returning, we should have both a course generator and a course maker, and have the course making tools done either online in-browser, or (preferably) available in the game for all players to access and use.