The posts I have read indicate that it is possible to take the Slashing Grace feat as a Swashbuckler in order to get DEX to damage with a slashing weapon.
As much as I like the idea I see the following problem. The Slashing Grace feat lists as prerequisite weapon finesse with the weapon to be used, in this case a slashing weapon. But the Swashbuckler finesse is only valid for piercing weapons. Therefore, strictly speaking, Slashing Grace could never be applied to a Swashbuckler with a slashing weapon.
On the other hand, the description of the Slashing Grace feat explicitly refers to the Swashbuckler class and states that "...you can treat it as a one-handed piercing melee weapon".
So, how do these two interact, what is the intention of the RAW rules?