I'm thinking of giving an extra fortune point but making them have particular flavours they must be used as when being used in order to encourage more narrative description.

Eg.., one or two are "terrain or physical features" and can be used if player describes how those help them such as getting the sun in the foe's eyes, one or two are "emotional and personal factors" and can be used when describing how you hate that creature or are striving to aid your friend etc.

Any could still be spent on the other uses of fortune points.

I want to encourage players to get in the habit of doing this sort of thing, which eventually would earn them bonus fortune points.

Any thoughts on the approach or suggestions for other categories of "player driven narrative"?

I tend to give fortune dice out to players whenever they roleplay their actions in an interesting, funny, or inventive way. I don't give them the bonus die every time they roleplay, but really only when I (and/or the other players) think it's deserved. But I don't keep track of these extra dice in any way.

I'm all for increasing the narrative of the game. I love how the die results tell a story and I think your idea really adds to this. I will be suggesting this to my GM today.

Thanks, let me know if you use it. I haven't started, still mulling and thinking of it as part of shift for next campaign when current one wraps.

Also been considering replacing Fortune Points with Plot Twist Cards (paizo). I used a homebrew version of this long ago (just after story cards came out, that Plot Twist admits inspiration from) but made mistake of letting the "plot twist" be "narrative or spend as mechanical bennie" rather than "doh, use as narrative intervention to authorize mechanical bennie".