Development funding for open source software should not be "fair." People who want it developed simply have to develop it themselves or pay whatever it takes for it to features to be developed.
If 50% of miners want a fund and 50% of miners don't, then let the 50% of miners who want it just pay 25% tax of their own money instead of 12.5% of everyone. Start a foundation with members/fees if you want to fund open source development.
Somehow things like Linux get developed just fine...