-Monza. I've been begging and pleading for a modern version of this track to be made for NR for the longest time. I even attempted on my own to do so a couple times to no avail. In my opinion, the GPL conversions available are not only outdated and inaccurate, they're also really ugly. NR could use something better.
-Devil's Canyon, from the EA NASCAR games. I remember racing on this track as a kid and being amazed by the scenery. I also remember making multiple threads on NNRacing circa 2009 asking for this track to be made, until it reached a point where people got fed up with me asking and flamed me for it. But still, eight years later, I'd like to see this track made. I would imagine that making .3DOs for all the rock formations on that track would be problematic, though.
-Speedway Blvd., also from the EA NASCAR games. I had fun driving on the roads surrounding the Daytona International Speedway, and I think this track could be feasibly done for NR. Though it might be something of a frame killer, I imagine.
-Rainbow Road, from Mario Kart 64. This was another track I'd attempted to make on my own for NR, but I got stuck on the elevation changes so I never finished it. Since this track was made for Assetto Corsa, I think it could similarly be made for NR, though from what I've been told, the upward spiral that track has might pose a problem in NR. I don't see why it would though, Green Valley 540 seems to handle it just fine...
-Complex String, from Gran Turismo 3. It's the mother of all technical courses. I don't think this would be too difficult to do as it is a pretty flat and featureless road course, it's more cornering-intensive than anything. I certainly think it would be interesting to see how well it translates to NR, seeing as how it's been made for GPL and rFactor.
-The Meadowlands Grand Prix circuit, using either of the two configurations that were used when CART ran there. Until Formula E runs in New York City this summer, this has been the closest any major racing league has gotten to a race in the city. I actually live about a half an hour's drive from the Meadowlands, so naturally I'd like to see this course become a reality in NR.
-Occoneechee Speedway and Asheville-Weaverville Speedway. I've grouped these together because I'm including them for the same reason: They both served purpose during NASCAR's formative years. And since we have a 40's NASCAR Modifieds mod in the works, I figure there should be a new track to accompany that mod's release.
-Some manner of board track, like the old, high-banked tracks made out of wooden planks in the 1920's, purpose-built for motor racing. In NR, this type of track would probably be nothing more than a goof track, but there's no reason not to make a track like this either.