It goes like this: you first run a test suite by means of the atf-run tool, then use the atf-report utility to convert atf-run's output to the new XML format and at last use a standard XSLT processor to transform the document to whichever other format you want. I'm including sample XSLT and CSS style-sheets in the package to ease this process.
I've uploaded an example of what this currently looks like, but be aware that this is still a very preliminary mockup. For example, adding more details for failed stuff is needed to ease debugging later on. Comments welcome!