WordPress Wireframing Kit
WordPress is so pervasive that 10up has created a set of WordPress widgets and templates for Sketch:
[…] which cover the breadth of WordPress’s authoring and administrative environment. Being able to start from this solid foundation allows us to focus more on the concepts and less on pushing the pixels to make it look like an authentic backend experience.
10up does some big WP installs (FiveThirtyEight, TechCrunch, etc.) so they would know.