I disagree - it ought to be possible to do it in OpenSCAD, but it would be a major effort.
The first step would be to get hold of the vertices and faces of the shape you want to voronoi. The .stl file contains the information, you would have to write the translator into a list intelligeble by OpenSCAD. Once you have that list. you can recreate your shape using polyhedron().
Since you now have the list of all vectors and faces, you can use Lloyd's algorithm (see https://en.wikipedia.org/wiki/Lloyd%27s_algorithm) to create new faces and voronoi to your heart's content.
It's a major effort, but - I would think - worth the time spent, as it allows the creation of porous objects, which is the area where 3D printing really excels in. Explore the website of http://uformia.com to see what is possible.
Visualise what it would mean for aircraft enthusiasts if they could print a wing or fuselage with a solid surface and a foam-like interior? How much rigidity would that add to their design, at how much weight? Ribs and struts are such poor replacements for an integral design . . .