For reasons that are probably out of scope for CSS, I would really like to be able to do more with the CSS content property.
It's one broad class of problem really: many frameworks make changing the HTML they generate difficult or impossible. Inevitably you end up needing to inject a button or a hyperlinked image or something in a particular position, and you have to resort to Javascript to do something that isn't interactive and isn't a program, which feels like the wrong tool.
You could argue that both Javascript and CSS are the wrong tool for this use case, but CSS would be the more convenient wrong tool.
