I believe that this phoronix article has some answers for you about wayland and screensaver.
This article mainly says that it will be more integrated :
> it can ensure that no window can appear atop the screensaver surface, it can properly detect idling and grabs already, and has complete control over the screen. **Unlike the X design** , there wouldn't even need to be a screensaver "window" that's on top but the compositor could just keep painting a black screen.
It seems to have been implemented 3 months ago. He writes that :
> This also causes properly written animating clients to stop rendering, and we can hit **zero CPU usage** , even when there is a screensaver active.