Here is how I fixed it, but unfortunately does not provide information as to what the issue actually was. I tried a few things but really am not entirely certain what the correct directories for the prefs etc. look like, so nothing worked. I suspect it was a permissions issue of some kind.
using the app “Find Any File” I searched out any file or folder that had Nuendo or Steinberg in the name and trashed it. Everything. Invisible files, logs, preferences etc. everything. The only exceptions were for files within the Eucon directory, or the Dolby directory which I left in place.
Empty trash, reboot.
Install Nuendo 8 but this time when it asks if I want to get a current update I say no. Install 8.0.
Launch 8.0 which runs a Fresh scan of all plug-ins.
Create a temp session with a couple dummy tracks. save it. Quit Nuendo.
Relaunch Nuendo and it opens as expected, does not rescan plug-ins.
Now I download the 8.3 update. Run that and relaunch Nuendo. It will rescan only the updated Steinberg plugs and that’s it. Opens quickly.
Problem Fixed. Back to work.