FORMAT=HTML available?

I looked through the documentation and source code, and it doesn't look like
there is a FORMAT=HTML.  Basically, there are a few html content checks that
I am doing with Hobbit, and I would like the emails that get sent out to use
the HTML MIME format.  It looks like the default MAIL output is plain-text.
Would it be possible to add HTML as an option for the FORMAT= command?