Hi JoeBlack,
Unfortunately I have to tell you that the thumbnail views won´t work functional currently. They are still there, as we offered an external server component some time ago, which was able to convert the document content into a thumbnail and then the thumbnail was displayed in those thumbnail views. In the examples, they just point to a hardcoded png file for every document.
BUT, I am glad to tell you that with the upcoming Workdesk 4.2.0.0 release we will bring back thumbnails again by making use of cmis:thumbnail renditions. Also we will offer preview functionality by using the corresponding rendition for that case. So there are great things coming concerning displaying content and previewing content. Stay tuned 🙂
Regards,
Dennis