Hamdown author here. To make it clear the I don't see this as a replacement for HTML/ERB/whatever templating solution for your web app.

The niche is rather narrow - it is for people who use static site generators like Jekyll/Middleman, and write content mostly in Markdown.

I often simply want to do a quick look-and-feel experiment by styling some of the elements with Tachyons. This is where Markdown becomes a bottleneck.

Another idea is to make front-matter a first class citizen of Hamdown so that you could add a bit of structured data on top of your blog post and use on the page.

P.S. You kinda can achieve this with kramdown, but I find its syntax super-weird.