The suggestion is to color the interwiki link differently, if on the linked page, there is a section related to the current language.
I'm on the French Wiktionary, on the page "pain". There is an interwiki link to the English Wiktionary because a page "pain" also exists there.
On this en:pain, there are several sections for several definitions in several languages. There is a section about French word "pain".
Then, on the French page, the link will be blue.
Otherwise, if no French section exists on the English page, then on the French page, the link to the English page will be (for example) green.
Use case : this inform the user that even if a page exist in another language, there is no section about his own language, then maybe he could go there and add it. It would encourage contribution and cross-wiki contribution.
This feature could be considered as a gadget.