InDesign has this in place, and so should Illustrator :)

When you import an image file into Illustrator and copy it, it will make a new copy, instead of a new instance. If you work on a file where an image file is included multiple times, the Illustrator file itself often becomes too large.

This would never have happened if the duplicates of the image file were instances instead of copies.

It is also impossible to relink duplicates of the same image when they are copies. You have to do it manually. It's both time-consuming and outdated.

Turning the image file into a symbol is not much of help either as it still creates a new link in the links panel!

Do as in InDesign. It will help reduce file sizes and improve performance!

Improved links panel. List all instances of a linked image under one 'primary' link, append the filename with " (xx instances) ". Use a chevron that points right to indicate that there are multiple instances under the "primary" one shown in the list. Clicking the chevron makes the chevron point down, and displays the list of all instances.

Clicking to select the "main" instance and clicking the re-link button should allow the user to replace all instances of the same image. Allow the user to expand the list downward as described above and select a single, or multiple instances to re-link. In this case, provide a pop-up dialog asking whether to relink all selected instances or re-link one at a time, incase the user wants to link different images.

If user relinks with different images, move those new links into their own instance grouping with a "primary" heading of its own.

Image mockup provided for clarity.

Illustrator think that updating a link is not an operation.
This leads to problems with documents that use PDF-compatibility option.

Imagine you have an already saved document that have some linked images in it. You open it in Ai and then Edit a linked image in Photoshop. Make some changes in the image, save them in Ps, go to Ai and agree to update the link...

But Ai still considers the document as non-'dirty', as if no changes were made.

You can’t save the document and re-write the PDF content, to see these changes appear, say, in the InD document, where this Ai-documnet is placed in another document. You can only re-Save-As is, which is a not convenient operation. And if you close it — Ai does NOT offer you to save! And you have a document that you though HAVE an updated image in PDF-layer, while in fact it does NOT.

InDesign treats this right in same circumstances.

Again, if you had an .ai document that uses a link, that has been updated before you open this .ai document — Ai will tell you nothing about the change, and you have a file that has two version of image — one in Ai layer, and one in PDF one.

Very error prone.