With screensavers these days being used more often to just lock the display when away from the computer or to show off interesting visuals around the office, the screensaver implementation for X right now is quite bad. In fact, we just talked at length about it last week.
The plans for the Wayland Display Server are to merge the screensaver with the Wayland compositor, so that the display can be properly locked and there's no chance of any of the screen's contents being painted atop the screensaver, as can currently happen with X. Martin's plans for KDE SC 4.8 are along the same lines with moving the screensaver into KWin so that the compositor has full control over it for ensuring the screensaver is properly displayed and nothing else.
This though will require some work, so it's a target for KDE SC 4.8 and not the next KDE SC 4.7 release. It will also require proper handling in cases where compositing is not supported or enabled and integration with certain Plasma features.
Read more about the plans on Martin's blog.