Currently if "Show pinned applications" option is enabled. It is applied to all monitors.
An option to show only the open apps on the Secondary Monitor, would make the secondary dock less cluttered.
As essentially right now, there is a duplicated, Pinned Dock
It would be something like this:
Before
Main Monitor
Secondary Monitor
After
Main Monitor
Secondary Monitor
Even an option for unique, pinned apps, per monitor/dock would be nice.