Started reading with interest, but then everything started to look really similar to HAML [0] after a bit. With the exception that HAML also lets you add CSS classes to your tags...
[0] - http://haml.info/
[0] - http://haml.info/
<s:tag name="note">
<div style="color:red;">
Note: {{@content}}!!
</div>
</s:tag>
And then call your new tag using the HTML syntax or Sundown: <note>Sundown is awesome ;)</note>
:note Sundown is awesome :)