Actually most of the work on IFC exporting is already done (
https://gist.github.com/yorikvanhavre/6040612 ). What still needs to be done is to fix some issues in ifcopenshell, and then make the interface between freecad and the ifcwriter module, but that should be relatively simple. Then we can already output valid IFC files.
Of course, the whole complexity, as Thomas Krijnen (the author of ifcopenshell) and I discussed already, is to export not only simply geometry to IFC, but also design intent, that is, how the geometry is generated (for example, if a wall is based on a center line, that has been given a thickness, then extruded, that whole information should also be exported to the IFC file so other software can recreate the wall the same way). But that is for a later stage...