As the subject asks, I REALLY liked using kio slaves over the years, the slaves made so many of my efforts so very simple.

I just installed Kubuntu, and after getting over the (insert disapproving term here) blah look of KDE 5, I was saddened to see that Dolphin does not support ripping audio CDs via kio slaves. I was already saddened to lose the configuration dialogs many months ago and I am aware of this thread: viewtopic.php?f=224&t=131038 so thankfully at least there is hope for me to boot a recent Kubuntu from a USB stick.

Thanks in advance, and if there is a better place to make the request, I'd appreciate a pointer to it.

Dolphin does (still) use kio slaves in its KF5 incarnation.
But the audiocd slave has just not been ported to KDE Frameworks5 yet.

Currently, for ripping audiocds you have to use konqueror or dolphin4 (both should still be available, on openSUSE the packages are called konqueror and dolphin4, might be kde-baseapps or similar though), or some other dedicated application.