I would seem that ConTeXt has a natural market in web developers who are used to writing structured documents for layout engines. Personally, I'd like to see a Drupal module that will ConTeXtify a person's website as a book or magazine for printing. How great would it be to have an automatically updating e-book for print and screen generated off your website's content based on your tags/taxonomy. Just add "FortheBook" tag to an article, and without one having to do any more, it will appear in the PDF available on the front page of your site. There is a LaTeX module for Drupal, but I haven't tried it. I think such a module would help to whet other web developer's appetite for ConTeXT.
Have you looked at http://wiki.contextgarden.net/HTML_and_ConTeXt which explains how Saji converted a wiki to (informl) to pdf using ConTeXt. I do not know about Drupal, but similar thing should work. There is also Pandoc which can convert Markdown syntax to ConTeXt. It can also convert html to markdown, so in principle you can use it as html to context converter. (Of course, with this approach you are limited to only things which markdown can capture). Aditya