I would like to propose a feature to toggle on visibility of 3D elements (at the cut-plane) when taking a section view, if it’s possible.
This would go a long way to understand the shapes (and aspect ratios) of meshed elements inside a solid as you move the cut-plane.
This is also possible in ParaView (postprocessing in FreeCAD FEM module is based on that software). If you want to give it a try just convert the .frd file generated by CalculiX to .vtk and use the Clip filter with the “Crinkle clip” option checked in ParaView.