Sorry to bump this thread out of the ground.
To have markdown rendered within HTML blocks, what is usually done in other Markdown dialects is to add a markdown=1
option in the html outer tag. An other solution retained in Github Flavoured Markdown is to add blank lines this way:
<div>
*Emphasized* text.
</div>
This kind of behaviour is currently what I need to render a gallery. I am doing it this way:
<div class="gallery" markdown=1>



</div>
Then trigger it with CSS.
But note that blackfriday has not implemented it for now.
My 2 cents.
EDIT: Here is a script to render a Markdown draft into HTML with pandoc. It accepts Markdown within a HTML block.