I've read the old posts on this, and I understand the problem, particularly as it pertains to Windows and licensing of some tool to render PDFs...
Nonetheless, I've been receiving image files lately that are in PDF format. These typically are documents that are image heavy, but also have text. Often photogs will have PDF brochures, for example. The previews show up fine in Finder. No surprise there. But I'd love to be able to see a thumbnail on PM's contact sheet. I'd want to rename and rate them. Perhaps rating and tagging the files could be handled solely by sidecar files.
Not a high priority, but I'm throwing it out there.