With this patch, it is possible to right-click on linked datablocks (in the outliner), and choose "Open in new Blender". A new Blender process is started to edit the library file, while a modal operator keeps running to monitor the subprocess. After the subprocess finishes, the operator reloads the library blendfile and finishes.
One thing I'm not too happy about is the fact that the "Open in new Blender" menu item is always shown. I've simply added it to the exisiting menu items for various datablock types. Ideally it should only be added when the right-clicked datablock is actually linked. I don't know if that's possible with the current menu structure, though.