Is a blank screensaver really the only option? I’d like to use a specific image bouncing around as a screensaver. Is there any way to do this?
Dom0 runs xfce by default. You should be able to install screensavers in it:
But be careful: any malicious package in dom0 leads to the full system compromise: Security-critical code | Qubes OS
Qubes ships a version of XscreenSaver - you can configure it from the
xscreensaver-demo command in dom0, and configure under the
DisplayModes tab.