@stumpi KDE is great in 4.1 But you need to install it differently than the official docs instructions.
Use the following:
sudo qubes-dom0-update apper breeze-icon-theme colord-kde dolphin kcm_systemd kde-runtime kde-settings-pulseaudio kde-style-breeze kdelibs kdeplasma-addons kdialog khelpcenter khotkeys kinfocenter kmenuedit kmix konsole5 kscreen ksysguard kwin phonon-qt5-backend-gstreamer plasma-breeze plasma-desktop plasma-desktop-doc plasma-pa plasma-user-manager plasma-workspace polkit-kde qt5-qdbusviewer sddm sddm-breeze sddm-kcm sni-qt
And then reinstall the same thing immediately:
sudo qubes-dom0-update --action=reinstall apper breeze-icon-theme colord-kde dolphin kcm_systemd kde-runtime kde-settings-pulseaudio kde-style-breeze kdelibs kdeplasma-addons kdialog khelpcenter khotkeys kinfocenter kmenuedit kmix konsole5 kscreen ksysguard kwin phonon-qt5-backend-gstreamer plasma-breeze plasma-desktop plasma-desktop-doc plasma-pa plasma-user-manager plasma-workspace polkit-kde qt5-qdbusviewer sddm sddm-breeze sddm-kcm sni-qt
Then reboot the machine and click the upper right hand corner of the screen at the user login and select “Plasma”.
[source: KDE - changing the way you use Qubes - #8 by Sven]
Enjoy!