This would be a joint effort between AI and INDD. But being able to assign a spot color swatch placeholder to a graphic like any other spot swatch (with tint support) that can then be assigned via the links panel in InDesign.

Often I need to color coordinate graphics with a document I am building in InDesign. I typically do this by either generating multiple artboards or layers with the variations I need. But sometimes for one-off projects or projects where there may need to be many variations it just makes the AI file much more cumbersome to deal with.

If I could assign a spot color in AI and then in INDD alter/adjust that color definition (ideally per instance but even just per link) that would be awesome. Then it would export and be read by Acrobat or other RIP software as if it was the spot color I assigned.

Additionally this placeholder functionality should pass through when saved as an Illustrator native PDF (.ai.pdf files are so much more versatile in InDesign than .ai files)