@geier, no.
The only unusual repo I have on the system with the removals is the skype-stable repo at repo.skype.com.
EDIT: Since it seemed like my problem was not experienced by anyone else, I decided to let the full-upgrade go through and then try to fix the damage. The nvdia-related packages that include "-glvnd-" were part of the problem -- apparently they are not required and conflict with a lot of qt5-based packages. Nvidia driver 375.82-4 is reinstalled and working correctly, as is ffmpeg, vlc, and phonon-backend-vlc. I don't need cheese any more. So, sorry for the noise!