Any other ideas? I just did a du today and now have a plasma crash dialog and a black screen. I've tried renaming plasma-desktop-appletsrc but that did not help. (Edit) Renaming .kde/share/config brings back kde, I haven't found which files have the problem but it was not any of the plasmarc files.
After copying some files over bit by bit and trying to keep track of them, I have some instability with plasma crashing periodically but recovering. I can't tell which files were the ones that introduced the instability.