Problem: It is extremely cumbersome to find out who wrote a specific part of the article, get an overview of how the current content maps to the various authors etc. History search based tools like WikiBlame make it merely very cumbersome. Who Wrote That? is a tool that provides a decent experience, but it is only available at a select few large Wikipedias.
Proposed solution: Extend Who Wrote That? to more wikis.
Who would benefit: Editors who need to track down problematic (or particularly excellent) content, wiki historians, researchers, readers suspicious about the reliability of a page etc.