Hi,
Just made a little add-on to work easily with pose library.
It allows to work easily with linked/proxified armature.
Basically, when you work with proxy armature, set the linked pose lib in the poseLibrary input.
You can add/renam/delete poseLib in the linked one using blender shortcut (Shit/ctrl/alt + L).
The problem is when you save/re open the file, the new poselib you created are gone (or you have to make poselib local and then re append it in the original character file etc etc… boring work)
This add-on add an “Export” button that update the original blend file with newly created poseLib (so you can update it easily while animating).
It’s a v1, let me know if you have issue 
boby