I've been looking at using the method of "Advantage" from Revolution d100 while also keeping the Critical/Fumble mechanic in place. Advantage is any time the tens digit exceeds the ones digit. This would mean a 50% skill will still crit on a roll of 1-5, but also get Advantage (or Special success if you like) on rolls of 10, 20-21, 30-32, 40-43. I think this could be used for an extra level of failure as well, though I'm personally comfortable with simple Failure and Fumble. I haven't play tested this yet, but the numbers look pretty fair to me.