The title really says what I’m looking for. Recently completed features that I thought were getting close to solving this include:
- Keep symbols as symbols when pasting between documents: DONE.
- Name symbols: DONE.

But-- what I'm looking for is the ability to paste symbols between XD documents without the symbol being duplicated. I'd like it to detect that the new document already has a symbol with the same name as the one being pasted in, and prompt me, letting me choose between:
1) Use symbol in current document
2) Replace symbol in this document with the one being pasted
3) Create a new symbol (and possibly add a (1) at the end of the name or allow me to give it a new name.)

Currently, it just adds a new symbol with the same name, over time resulting in many, many symbols that look the same and have the same name. Especially when these symbols contain images, my files end up bloated because every time I copy an artboard from one file to another, it creates a new instance of all the symbols on that artboard. Cleanup is futile, because these symbols keep getting duplicated each time I paste between documents. Working with a team of designers on a large project, it's just not practical to do all of our work in one file, so copy/pasting artboards and design elements between files is a crucial part of our workflow.

To cut down on over-prompting, you could consider only prompting for symbols with custom names. If the symbol hasn't been renamed (e.g. Symbol 2) consider not prompting since the user isn't carefully managing unnamed symbols anyway.

I hope that your solution for this is not to rely on the CC Library, because my company (and many other large enterprises) blocks our use of the Adobe cloud.

In the meantime, if we at least had the ability to select multiple symbols and do a "Highlight on Canvas" for all of them at the same time, it would speed up my cleanup process. But as it is, I just don't have the time to clean up what will just become a mess again, so I have no reason to use symbols at all.

Attached is a short video clip showing what's happening, as well as the XD files I used to create the movie.