[stevekemp]

Off the top of my head I was thinking of lack of moderation, and spam problems.

There's also a lack of formatting, but perhaps you could just not show posts without a header containing "text/markdown", or similar, to work around that.

Binaries would be grossly inefficient too, if you resorted to multipart-posts with encoded bodies. Again that could probably be worked around - either use single-post parts only, or ignore them entirely as you preferred.