I'll make some suggestions.

 

Temporarily Boolean off the leading edge of the wing, where it is much wider than .4 mm, so that the top and bottom
curves of cross sections will be separate.

Do a bunch of cross sections leading edge to trailing edge. Lineweb and Project might help?

Max has a script _CMorph to find curves in between two other curves. Make a center curve with an odd number, eg 3.

For each cross section, copy a 4 mm line, by center point, say perpendicular to center curve, to where it touches the top and bottom curves.
The centerline will be at the center curve. How to get it in the right location?

Sweep a vertical line along these points to make a trim surface...

...?

- Brian