Meme Dissident in Exile...
Fascinating. In that case, here would be my proposal to revive shuffle races using the more current system... First off, the Shuffle Base could be based around the power/weight ratio, rather than PP or category, and would be set as the approximate mean of the cars' p/w ratio.
I had a similar idea. There's no real need for potential Shuffle in GTS to stick to the N Class system. A power to weight ratio system would work just as well, if not better. I updated the OP with this idea.
In GT Sport though, it wouldn't be as good simply because there is less road cars variety, and they are more spread out in terms of lap times. I did test all road cars from GT6 and GTS, in the former you can find groups of 10+ cars within a second or less. GTS, you may find 2 or 3 if you're lucky. Shuffle could kinda work in Gr.3, Gr.4 and Gr.B but it wouldn't really be the same stuff.
I had an idea to increase the number of cars, without actually increasing the number of cars. There are 4 levels of upgrades for each car in GT Sport, so create duplicates of every car each with a different power & weight set up. That would make about 6 different versions of each available car, thus upping the pool of cars for Shuffle Mode.