opennurbs_offsetsurface.h as the following comment:
// This is still a work in progress. In particular,
// this surface class can not be saved in files, used
// as a brep surface, added to Rhino, etc.
// As of January 2004, it is useful for calculating
// offset meshes and any other fitting and approximation
// tools that requires a surface evaluator but do not need
// NURBS forms, isocurves, and so on.
Is this really still the case 15 years on?