Alfred,
I know I answered this in your personal post but I will go ahead and answer it here as well...
To give you some perspective on why it has replace FBX import/export for me, I am a tradesperson who does BIM VDC work fulltime for a contractor. I work primarily out of Navisworks (for coordination with other trades) and AutoCAD. We would regularly use FBX export from Navisworks in order scavenging design model valves/components/equipment/vessels/steel or any other model content that we were not provided in DWG form and import them into AutoCAD. I am not sure of your use of FBX other than to import to Civil 3D from infraworks, but when FBX import capabilities were removed it disrupted our workflow for accessing this geometry from Navisworks to AutoCAD. Could we manage to bring them in by converting the FBX to DWG with 3DS max? Sure, but it was not very streamline and if one did not have the AEC license bundle they would have to purchase additional software.
I hope that I did not offend anyone by posting this here, I just it might help some folks. Will Navis to Acad be beneficial in your personal workflow? Maybe. Could it benefit other folks who are using Navisworks along side AutoCAD who stumble upon this thread? I would bet on it.