I know it's possible for an Estoc to have dex modifier for damage with the 'Agile' Magic Weapon Special Ability but I was wondering if any of the following options would allow the same ability:
Your dashing style and fluid rapier forms allow you to use agility rather than brute force to fell your foes.
Benefit(s): When wielding a rapier one-handed, you can add your Dexterity modifier instead of your Strength modifier to that weapon’s damage. The rapier must be one appropriate for your size. You do not gain this benefit while fighting with two weapons or using flurry of blows, or anytime another hand is otherwise occupied.
In addition, if you have the panache class feature, you gain a +2 bonus to your CMD against attempts to disarm you of your rapier while you have at least 1 panache point.
or
You can stab your enemies with your sword or another slashing weapon.
Benefit: Choose one kind of light or one-handed slashing weapon (such as the longsword). When wielding your chosen weapon one-handed, you can treat it as a one-handed piercing melee weapon for all feats and class abilities that require such a weapon (such as a swashbuckler’s or a duelist’s precise strike) and you can add your Dexterity modifier instead of your Strength modifier to that weapon’s damage. The weapon must be one appropriate for your size.
You do not gain this benefit while fighting with two weapons or using flurry of blows, or any time another hand is otherwise occupied.
It seems like none of these work because Fencing Grace works only for Rapiers (although could someone consider an Estoc to be a type of rapier?), and Slashing Grace wouldn't work because Estoc is piercing.
Best Answer
No, it doesn't work.
But with the Weapon Versatility feat (requires Weapon Focus) from the Undead Slayer's Handbook, you can use the Estoc with Slashing Grace just fine.
However, there are other options that you can look into:
Mythic Weapon Finesse - only available if you have mythic. Allows the character to add dex to damage to all finessable weapons.
4th level of a swashbuckler archetype called Whirling Dervish. This applies to all weapons that work with Swashbuckler finesse plus scimitars.
Finally, if the Path of War from Dreamscarred Press (third party publisher) is allowed, you have Deadly Agility, which allows you to use dex to damage on any light or finessable weapon.