Use case or problem
The pinned note feature lacks utility.
Proposed solution
It will be good if pinned note is accessible every time easily.
This can be made possible by rendering a floating bubble of such pinned note on closing it. That bubble will float above the UI anywhere.
Alternatively:
There could be a in-app floating dock like Rocket Dock which will hold any open note (pinned or not) which is minimized.
Such mechanism may serve an alternative to Sliding Pane or Maximise Active Pane plugin.