We need a set of feats that work with something that isn't a bastard sword or dwarven axe to boost, however minimally, duelist / swashbuckler style.
It can be a feat-chain like TWF, ITWF, GTWF or THF, ITHF, GTHF but should instead provide a doublestrike boost or a precision damage boost, something. Maybe it only works with finesseable weapons, heck maybe the first feat in the chain is finesse. Whatever.
I want a reason to use a rapier + a buckler, other than comedic value.