The same small list appears in several articles. Panoramas, inline videos, and articles with PDF image format are not support on Android. For HTML, the Android devices use a different browser than mobile Safari on the iPad, so Web Content overlays and HTML articles can differ.
Also, some mp4 h.264 videos that work on the iPad don't work on Android because the video doesn't use the baseline profile.
I searched the publishing companion guide, this site, and Google, before submitting this question and found nothing. I know I had seen it before but the development of this product moving the way it does, I wanted a definitive answer. Not something from an "article" from last year.
The iPad publishing companion guide doesn't have this information, but the Android publishing guide (http://helpx.adobe.com/digital-publishing-suite/kb/publishing-process- android-amazon-mobile.html) does.
This information is also mentioned in the Android preview help topic as well as the authoring for multiple devices topic. But it sounds like I need to create a new topic called "Supported Android features." I'll do that.