I'd love to see this plugin search for a "changelog.md" or similarly-named files too. I always include this in my themes.

Until we get WordPress.org support for it, change logs aren't going to be in most themes. And, to be honest, the biggest issue is going to be not breaking stuff if/when .ORG adds support for a "readme.txt". There are many themes with this file, but the formatting is wildly inconsistent because of the lack of a standard.