Icon thumbnails in card view

[ryanleichty]

I noticed a particular behavior with card thumbnails within a matrix field. If the first card you add has a thumbnail, the thumbnail will display. If the first card doesn't have a thumbnail (like this text entry type), any subsequent cards won't display a thumbnail whether they have one or not. I feel like this is a bug, but maybe it's the intended behavior? (edit: moved to #16682)

Aside from that, what I really want is for cards without a thumbnail to show the entry icon. This was previously illustrated over here.