The other day I wrote about the Pager improvements awaiting in Plasma 5.8. In the comments user btin re-raised the issue of limiting the Pager's display to the screen it's currently on, instead of being all-exclusive.
At the time I wasn't sure we could still sneak this in before feature freeze, but thanks to the screen-awareness of the new backend (which, to recap, is shared with the Task Manager and already needs to determine what screen a given window resides on), it turned out to be easy enough to do!
The default remains the screen-spanning behavior for now, but in the Pager's "Display" settings you can now tick a new "Only the current screen" checkbox. If enabled, Pagers in panels on different screens will now nicely be limited to showing their respective screen's windows on each desktop.