Bundle a separate application for previewing files as HTML

There seems to be an aversion to putting too much functionality into Sublime. Then how about a separate application? It would show a single browser window and watch a directory. You would be able to configure what files are watched and how they are converted to HTML. It should be possible to optionally make that conversion without creating files, by writing to stdout.
Example configurations:

• HTML: Watch all .html and .css files. If one of them changes, reload the browser window.
• AsciiDoc: Watch all .asc files. If one of them changes, convert it to an HTML file and reload the browser window.
• Markdown: Watch all .md, .mdown and .markdown files. If one of them changes, translate it to HTML and pipe the result to the browser window.