Ah I miss-read what you where after. Something like this $report.content_type === 'post' && $report.Content && $report.Content.isFirstPost() will be a report for a Thread while things for a post are just for $report.content_type === 'post'
Yeah, I think it just wipes all custom fields. I'll need to add an option to control which custom fields it wipes (or doesn't wipe) as determining what is "viewable" is frankly tricky.