Downgrading dolphin (to 4:15.4.3) but keeping konqueror at 4:15.08.1-1 allows to use dolphinpart again.
During the update from 4:15.4.3 (working) to 4:15.08 (broken), dolphin was split to a separate src package and its libs were moved to a different folder (from /usr/lib/kde4 to /usr/lib/[ARCH]/qt5/plugins). Maybe it's looking for the dolphinpart.so in the wrong folder? However, just symlinking dolphinpart.so to the old path does not work for me
