As of Tumbleweed update this morning (first run for 2 weeks or so), the system tray power management icon is missing and I cannot change screen brightness (hot keys nor any software I can discover), which seems set to some middle level. Accessing Power Management in System Settings returns
Power Management configuration module could not be loaded. The Power Management Service appears not to be running. This can be solved by starting or scheduling it inside "Startup and Shutdown"
There is no Power Management Service in Startup and Shutdown.

Investigating possibly related bits of systemd I find the wonderfully named

systemd-backlight@backlight:intel_backlight

But this restarts without error and seems happy on a status query:

Code:
# service systemd-backlight@backlight:intel_backlight status
● systemd-backlight@backlight:intel_backlight.service - Load/Save Screen Backlight Brightness of backlight:intel_backlight
   Loaded: loaded (/usr/lib/systemd/system/systemd-backlight@.service; static; vendor preset: disabled)
   Active: active (exited) since Sat 2017-04-01 12:34:23 BST; 8min ago
     Docs: man:systemd-backlight@.service(8)
  Process: 7564 ExecStop=/usr/lib/systemd/systemd-backlight save %i (code=exited, status=0/SUCCESS)
  Process: 7567 ExecStart=/usr/lib/systemd/systemd-backlight load %i (code=exited, status=0/SUCCESS)
 Main PID: 7567 (code=exited, status=0/SUCCESS)

Apr 01 12:34:23 linux-d3ee systemd[1]: Stopped Load/Save Screen Backlight Brightness of backlight:intel_backlight.
Apr 01 12:34:23 linux-d3ee systemd[1]: Starting Load/Save Screen Backlight Brightness of backlight:intel_backlight...
Apr 01 12:34:23 linux-d3ee systemd[1]: Started Load/Save Screen Backlight Brightness of backlight:intel_backlight.
Digging around logs can see nothing that looks abnormal during the post-update boot.

Any ideas?