I've seen more than a few kimchi fridges in use, and haven't seen one used for general purpose storage. Kimchi fridges, especially the chest type, are designed to be efficiently filled with uniform-sized containers, which would be very inefficient for random groceries and leftovers.

As far as being "an essential household fixture in most Korean homes," maybe I travel in the wrong circles, but I don' recall seeing them in many homes of the under-50s.