1. Highlight code interrelations. Example: click in a function, and the UI displays related code, along with indicators of the timing of relation (e.g. caller vs. callee), type of relation (e.g. override v. delegate v. strategy), strength of relation (e.g. 80% of the time function "f" is called, then function "g" is called), etc.
2. Collaborate on code reviews. Example: when I do a pull request, then I want to see my team's comments within my typical editor, within my real source code, rather than in some project management tool or some git hosting web page.
3. Make it much easier to write good documentation by automating feedback. Example: when anyone in the world uses my open source, and it doesn't work the way it's documented, then make it easy for the user to provide diagnostics directly to the section of code that's having the issue, suitable for triage by me.