I like this more than you'd think; my whole website is an extended exercise of Doing Cool Stuff with CSS and HTML generated from Markdown, but I always feel a little uncomfortable doing anything too fun when userstyles are not common practice. I could totally create a style switcher with Javascript, but... wouldn't it be better if that were built into the client?

Reader mode in Firefox is what I'd like to fall back to, but it doesn't handle my footnotes right now. :(