Description
Does this feature exist in Emacs orgmode core?
Yes
Orgmode link
When you do org-insert-link the first autocomplete orgmode would do is for handlers. So for instance you'll get options such as "file, http, ftp" etc. as well as any custom handlers someone may get
When someone selects that handler they will also get the custom autocomplete for that handler function. So for instance if you select the file handler you will get autocomplete for files relative to that directory.
Feature value
This would be useful since when theoretically custom link handlers are added, people will be able to add their own custom autocomplete for links.
Additional context
I think this would be useful for making the linking experience more similar to org-mode. Another issue that could be filed separately is creating files that do not exist when opening a linked file at a point.
I'm also looking to work on these tasks in the coming weeks if you don't mind.