I have created a patch for xfce4-panel that adds abbreviated vm names to the tasklist. Thought it would be helpful to share.
This is what it looks like:
You can download it here. The tar archive contains the compiled libtasklist.so the only relevant file that needs to be replaced and the only changed file tasklist-widget.c with edits to xfce_tasklist_button_name_changed and xfce_tasklist_get_qube_prefixed_name added. It is for 4.3.
You can compile it yourself using docker and replace /lib64/xfce4/panel/plugins/libtasklist.so on dom0.