We want to filter out the folder nodes (and other ones that definitely aren't involved into thumbnails display).

In order to do that we can do either of the following probably:

• assing a fixed filter on the JCR thumbnails presenter
• ensure that views are allowed to have the datasource defined for them and allow the thumbnails view get its own datasource that stems from the one of sub-app but filters out the folders.

I'd personally probably prefer the first approach (maybe experiment with definitions and introduce the JCR thumbnail view definitions with JCR-specific filters configurable).

Alternatively we can show preview for folders (just an icon or an asset from the folder)