It is a regression associated with KF5.
Command kdesu konsole do nothing. 

Reproducible: Always

Steps to Reproduce:
1. Launch command "kdesu konsole"

Actual Results:  
Application not launched at all.

Expected Results:  
Window with konsole root mode.

mar 11 09:46:03 arch kdeinit5[2086]: kscreen.kded: Change detected
mar 11 09:46:03 arch kdeinit5[2086]: kscreen.kded: Saving current config to file
mar 11 09:46:03 arch kdeinit5[2086]: kscreen.kded: Calculating config ID for KScreen::Config(0xb12a50)
mar 11 09:46:03 arch kdeinit5[2086]: kscreen.kded:         Part of the Id:  "a8d88c303a8b6f84f5bdbe109cf48311"
mar 11 09:46:03 arch kdeinit5[2086]: kscreen.kded:         Config ID: "65df2f41ea2a21320bf54e8f60bc5972"
mar 11 09:46:03 arch kdeinit5[2086]: kscreen.kded: Config saved on:  "/home/tomasz/.local/share/kscreen/65df2f41ea2a21320bf54e8f60bc5972"
mar 11 09:46:15 arch su[29419]: (to root) tomasz on pts/5
mar 11 09:46:15 arch su[29419]: pam_unix(su:session): session opened for user root by (uid=1000)
mar 11 09:46:15 arch su[29419]: pam_unix(su:session): session closed for user root
mar 11 09:46:15 arch kwin_x11[2213]: QXcbConnection: XCB error: 3 (BadWindow), sequence: 17212, resource id: 88080398, major code: 18 (ChangeProperty), minor code: 0
mar 11 09:46:15 arch su[29423]: (to root) tomasz on pts/5
mar 11 09:46:15 arch su[29423]: pam_unix(su:session): session opened for user root by (uid=1000)
mar 11 09:46:15 arch konsole[29429]: QCoreApplication::arguments: Please instantiate the QApplication object first
mar 11 09:46:15 arch konsole[29430]: QDBusConnection: session D-Bus connection created before QCoreApplication. Application may misbehave.
mar 11 09:46:15 arch su[29423]: pam_unix(su:session): session closed for user root
mar 11 09:46:15 arch kwin_x11[2213]: QXcbConnection: XCB error: 3 (BadWindow), sequence: 17365, resource id: 98566145, major code: 18 (ChangeProperty), minor code: 0
mar 11 09:46:15 arch konsole[29430]: QXcbConnection: Could not connect to display :0
mar 11 09:46:15 arch kwin_x11[2213]: QXcbConnection: XCB error: 3 (BadWindow), sequence: 17369, resource id: 88080399, major code: 18 (ChangeProperty), minor code: 0
mar 11 09:46:15 arch kscreen_backend_launcher[2299]: kscreen: Primary output changed from KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" ) to KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" )
mar 11 09:46:15 arch kscreen_backend_launcher[2299]: kscreen: Primary output changed from KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" ) to KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" )
mar 11 09:46:15 arch kscreen_backend_launcher[2299]: kscreen: Primary output changed from KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" ) to KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" )
mar 11 09:46:15 arch kscreen_backend_launcher[2299]: kscreen: Primary output changed from KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" ) to KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" )
mar 11 09:46:15 arch kdeinit5[2086]: kscreen: Primary output changed from KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" ) to KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" )
mar 11 09:46:15 arch kscreen_backend_launcher[2299]: kscreen: Primary output changed from KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" ) to KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" )
mar 11 09:46:15 arch kscreen_backend_launcher[2299]: kscreen: Primary output changed from KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" ) to KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" )
mar 11 09:46:15 arch kdeinit5[2086]: kscreen: Primary output changed from KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" ) to KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" )
mar 11 09:46:15 arch kscreen_backend_launcher[2299]: kscreen: Primary output changed from KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" ) to KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" )
mar 11 09:46:15 arch kscreen_backend_launcher[2299]: kscreen: Primary output changed from KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" ) to KScreen::Output(Id: 67 , Name: "LVDS1" ) ( "LVDS1" )
mar 11 09:46:15 arch systemd[1]: Created slice system-systemd\x2dcoredump.slice.
mar 11 09:46:15 arch kdeinit5[2086]: kscreen.kded: Change detected
mar 11 09:46:15 arch systemd[1]: Started Process Core Dump (PID 29436/UID 0).
mar 11 09:46:15 arch systemd-coredump[29437]: Can't open coredump directory: Not a directory
mar 11 09:46:15 arch systemd-coredump[29437]: Core Dumping has been disabled for process 29430 (konsole).
mar 11 09:46:15 arch systemd-coredump[29437]: Process 29430 (konsole) of user 0 dumped core.

#### packages ####

$ pacman -Q|egrep -i 'systemd|konsole|knotifyconfig'
knotifyconfig 5.19.0-1 ## KF5 5.19.0
konsole 15.12.2-1
lib32-systemd 229-1
libsystemd 229-3
systemd 229-3
systemd-sysvcompat 229-3