The process to create libraries is too bureaucratic and demands that I have to use the cloud... The cloud is fearly new and very unstable, lacks a lot of features other clouds have and it is prone to bugs. I really don't want to be forced to use it just to link assets between 2 files for one job. The library concept seems good and all, but it's not well done and very dependent on the buggy-limited-creative cloud. So, why not give an option to save a library as a local file, like a group of brushes in photoshop? We import it into the new file and use it. It is a fail safe as well in case the cloud has one of its many bugs.
*Bonus if the ui to create and import the libraries becomes more friendly, because right now I don't have the time nor disposition to read lots of texts to know what went wrong with my assets or how to do everything in it, really. I took a look in the user guide about this matter and I was tired in the first paragraph today. Some days ago, I managed to read some pages in search for a solution and the guide was useless, ver shallow on important things - it looks like more propaganda than a tool for us. I would suggest keep the most important functionalities in separate topics, very concise and straight forward on how to use.
XD has Document Assets and Cloud Libraries. In the Document Assets assets are stored in your local file. You can then copy and paste components into other documents and XD will link to them. If you don't want that link Right-click on the component and say Make Local. While this isn't everything you're asking for, I hope it helps.
If you'd like to see full local libraries, head over to https://adobexd.uservoice.com/ which is where you can search for existing features request and upvote them, or create new feature requests.
Adobe Certified Expert & Instructor at Noble Desktop | Web Developer, Designer, InDesign Scriptor