Thanks to the work of Korama, tech member over at Sonic Retro, and some additional help on finding the old shader files from Lobotomy, a new renderer is discovered, totally unused on the retail version of the game! It's still a bit too broken to be used, but it can do effects like directional shadows, better color correction, higher quality motion blur, working ice shaders, and even godrays!
Skip to about 1 minute into the video to see Cool Edge with this new renderer. Notice the dark shadows are just a bug with the renderer, and hopefully it can be fixed.
The use of this renderer won't be mandatory for the mod users, but it's still a possibility worth looking at. Be sure to check out the channels of the modders who made this possible as well!