My principled objection to Markdown
mbutterick.github.io
mbutterick.github.io
Of course, there are a lot of template languages out there: http://en.wikipedia.org/wiki/Comparison_of_web_template_engi... and I don't know how yours compares to the best of them, but the problem you're tackling is different from the problem that Markdown is tackling.
Let's not forget all the static site generators: http://staticsitegenerators.net/
The main strengths of Markdown are simplicity, readability, and standard feature set. Markdown is entirely usable without being transformed into HTML. Plus, the lack of extensibility means that services like GitHub can enable pretty views of Markdown documents without having to process costly and/or dangerous user-provided extensions. Once you introduce variables and calculations and lookups into a DOM, you largely lose all that and you have something entirely different.
*This is italic.*
<i>This is italic.</i>
or (semantic version): <em>This is italic.</em>
The second has three times the markup overhead as the first and the third has four times the markup overhead. That matters. If you're writing long-form text it matters a lot.Learning HTML doesn't help people who want to stay in the text editor.
Markdown however would be very useful in replacing the groff code used in man files for example, if perhaps it were a little more expressive - it has the advantage of being easy to parse when not render, and easy to build a renderer for.
So you get something that's easy to write, works with plain text formatting, and can be viewed with full HTML styling.