That gravelmap program is pretty cool, you just have to watch out as some of the routes people have put on there are for bike races and they are not all gravel, but this may just be a problem in the Zionsville/Indy Metro area. I added 34 miles of gravel in my county (Boone) the night I was told about it by the OP, but on a FB thread.
I would love to help develop this route, but I think it some coordination between participants would be nice to keep redundancy at a minimum, i.e., if someone in Fountian County already knows a route through it, why should I go randomly driving around to discover it? I know some of that is half the fun, but it could get pretty tedious as well.
I'm totally down to try and help!