Ok, I can report back that
a) Changing my install from freecad-python2 (which was chosen by default when installing freecad package on 18.04) to freecad-python3 (and of course removing freecad-python2 and all otherwise unused dependencies) works with the old OpenSCAD 2015.03-2+dfsg-2~18.04 from their PPA (which has not been updated yet, unfortunatelly)
b) it works with a simple example (cube/sphere difference) but with my initial meshes their seems to be another issue most likely with the mesh itself I assume (OpenSCADUtils.OpenSCADError: ' ERROR: CGAL error in CGAL_Nef_polyhedron3(): CGAL ERROR: assertion violation!\nExpr: e_below != SHalfedge_handle()\nFile: /usr/include/CGAL/Nef_3/SNC_FM_decorator.h\nLine: 426\nCurrent top level object is empty.\n'). Will further dig into that.
Two thing I'd suggest for improvement:
- Whether to fix the python2 variant or not (I understand that it might not be worth the effort) it would be nice that, if possible (depending on system), the python3 variant is installed by default.
- For the new error, it would be nice to not just see the same 'Unknown error' dialog in Mesh Design but a more telly one. OpenSCAD view shows the error on the output window which, I guess, was activate by myself otherwise it would have been quiet.
Just thoughts, trying to improve this cool piece of software.