I know this has probably been suggested to hell and back, but I would love some way to load shaders without using optifine.
Sodium uses a polyform shield 1.0.0 license:
https://polyformproject.org/licenses/shield/1.0.0/
Oculus uses a GNU lesser general public license:
https://www.gnu.org/licenses/lgpl-3.0.en.html
I know that the complete overhauls done between vanilla 1.12.2 and even the earliest versions those mods are available for makes this more of a "starting from scratch" rather than a backport, but there isn't really a 1.12.2 equivalent currently available, from what i can tell.