Maybe I'm reinventing the wheel but I've found that a household flatiron will do a perfect job of straightening saddle hackles and mallars flank feathers that have curved spines or cupped barbules. Put a moistened feather on the inoning board,convex side up, hold the feather by the stem, press the hot iron on top and pull the straightened feather out. For me it's a breakthrough.
P.S. I also "steam" chenille and poly yarn.