While not a permanent solution, I think a good step forward would be a refundable deposit fee for WAG bags, similar to the deposit on cans and bottles. This wouldn't address the sanitary concerns, but it would help reduce the eyesore of bags left abandoned by the trailside. Some people would still litter, but others who didn't mind the yuck factor would pack out a few extra bags and help keep the trail clean in return for getting the deposit fees.