This looks nice; I'll have a play when I have some time. One thing that's not immediate clear from the examples: how (if at all) are you avoiding Flash-Of-Unst

This looks nice; I'll have a play when I have some time. One thing that's not immediate clear from the examples: how (if at all) are you avoiding Flash-Of-Unstyled-Content on initial load? Might it be better to put the markdown in a <noscript> block rather than (or as well as) a <textarea> when editing isn't required?