there should be a way to access this info, but I didn't force this because it is not as straightforward. Theoretically, you may be able to store these values in geo nodes as a custom named attribute on 'points' that are representing your curve.
Also your intuition is right, this functionality has been floated by the Blender dev team, but has been delayed over time. Making this extension has revealed to me why-- it's not as straightforward to do as I assumed, and could get especially tricky with volume fields. There would need to be a lot of difficult decisions made on parsing and format. We may get this as a built-in function eventually, but I think requires more stability in geometry nodes to be full featured.
Perfect, I am surprised this isn't already a function within Blender.
Is there a way to do this for curves and instances along curves with stored attributes (Index, Location, Tangent etc)?