As a developer who works in WordPress, I find it usually quite easy to build a site and don't encounter many problems on this front; where I encounter many, many problems is when I have to edit / modify content on sites that my company had built before I had come on board, and try to figure out what insane way the page content is being generated on that particular site.
Something that seems so simple and yet is by far the hardest thing I have had to do while making edits is finding out how WordPress is generating a page and where the corresponding files are. Simply checking the templates / page.php / index.php files and so on usually does not yield many results. What would make my job and, I'm sure, many other people's jobs easier, would be a simple feature that prints out each file that WordPress is generating the page from as it does so, when it puts the content in, and so forth. Even just a simple list of the files used to build the page would make edits and modifications take one-tenth the time and one-tenth the frustration.
Please consider adding this feature or, if anyone has any suggestions for a plugin or something else along these lines, I am willing to try basically anything to attempt to circumvent having to do this again.