Turbinado sugar for pie

I think that a pie would be one of the few recipes where it wouldn't mess with the recipe too much; it just might not dissolve as well so you might get sort of uneven sweetness, but if there's any recipe where you can try it and see if it's too your liking, it would certainly be safe to try it in pie (or cobbler/crisp/crumble).

Absolutely! I sprinkle raw and turbinado sugar on pies, scones, croissants, etc. before baking and it keeps its texture but adds to caramelization. And adding it to the filling is certainly doable, but you tend to lose the nuance.

Yes; the sugar will dissolve in the filling. You could also do an egg or milk wash on top of the crust and sprinkle some on which would keep its crunch.

You certainly can, but it won't be crunchy... I'd suggest sprinkling the sugar over the top of the pie as soon as it comes out of the oven. The heat slightly melts the sugar but it retains its texture.