Wow! A chance to help out.
I am in. I am an environment artist and I have a good bit of experience with shader work in various engines.
Unfortunately we are in a bit of a crunch at work though so my time right now might be limited.
Do we have a rough Idea about when we want this taken care of?
Missed the last paragraph. I will get a clone and start getting familiar with the repo. Hopefully I will be able to contribute.
Just for a general approach though I would suggest we look into a systemic and iteration friendly approach through substance designer(Or painter, depending on how much of a re-work we want to do) doing one unit at a time will end up with inconsistent results.