A way to quickly change the default output is missing. One has to open the KCM and tick the default button for the respective device. Having the option to use the qdbus interface or a keyboard shortcut would be very nice. This option was present in the old kmix app, but is missing in plasma-pa, as far as I can tell. Reproducible: Always
It is now possible to change default device from applet in Plasma 5.10