Ok, so I went further and did a "zypper rm -u plymouth*" and "dracut --force" to ensure no trace was left behind, and continued to have no problems. Just now I uninstalled xf86-video-nouveau (followed by "dracut --force") and had the coredump (already posted) on first reboot. So in summary, if plymouth is uninstalled, and xf86-video-modesetting is used with a NVIDIA GTX 750, then the display manager will usually fail to load.