IMHO native support for showing backlinks would be a powerful upgrade to DEVONthink’s current WikiLink functionality as well as DT’s ability to help users find connections across different documents and ideas. I think most WikiLink users will welcome this feature.
To take this idea a bit further, it would also be nice to show a “local node graph” centered around the selected document, e.g. all the documents that are connected to the current document, and all the documents that are connected to those. I imagine such a local graph could have great potential to provide users insight on the current document. It’s like a graphical approach to the existing See Also & Classify functionality, but for explicit WikiLinks created by the user instead of content relevance calculated by the AI.
Recently there seems to be a surge of note taking apps that take the connections between notes seriously such as Roam Research and Obsidian, and the latter just released a Local Graph feature. I personally would be thrilled to see DEVONthink treat WikiLinks as a first class citizen, and automatic backlinks should be a very solid starting point 
Edit: here’s Obsidian’s Local Graph functionality in action.