Hi chenxi0987, upon reading your request, I thought I'd let you know that regardless if such a feature gets implemented or not. The functionality you want is still technically possible. 

You'd need to make your own pseudo libraries folder though and set it up accordingly using a software pointing to the folders in which you've included in Windows Libraries.

There is an open source software that can do this. It's called rclone. It's primarily a command-line program to manage files on cloud storage. I.e. allowing you to mount various cloud storage providers as a mounted folder on Windows, allowing you to browse, add, copy, edit and delete your cloud storage files as if they were on your computer themselves. Just like Onedrive, etc. In terms of cloud storage, I actually use in replacement of One Drive, Google Drive etc. I do this because it's a really lightweight program that can deal with multiple cloud storage vendors. Rather than have several softwares for each vendor on my system. Some of which are bloated software. I can just use a single piece of software dealing with many providers at once.

Although it's primarily for cloud storage, it does have a Union filesystem capability. Which you can merge several folders, either cloud storage or local directories and mount them onto another folder, so they appear as one. So you cloud make a pseudo Libraries folder and point Fences folder portal to that folder you've created. 

Here is the link to the rclones functionality that could help with what you desire. Union

Hope this helps : )

Fyi, I'm in no way affiliated with rclone, it's just a software I use and like.