|Status:||closed (won't fix)|
I realize having autocomplete functionality was requested - #1169630: Linkit-style autocomplete widget - but my organization needs to have something in place sooner rather than later.
I've built out a (dev) module which adds autocomplete functionality to the "Title" of all link fields (at some point, it should be its own separate widget instead of altering the current link widget).
Selecting the node title will fill in the URL with "node/#" (we want to use "node/#" for internal links when possible, which avoids having broken links if a node's alias changes).
Eventually, supporting autocomplete for the URL field should be added, but a core bug (#93854: Allow autocompletion requests to include slashes) needs to be resolved before it will work.
I don't think this makes sense as its own module (I've just built it out this way for now), but it provides a starting point for adding autocomplete functionality.