Make the preview high-dpi aware.
We could easily keep the preview size under a value, like KIconLoader::SizeEnormous currently, but maybe bigger like 2 * KIconLoader::SizeEnormous.
But I think that letting the user choose for himself the size of the preview, base on the size of the panel, is a nice feature.
I noticed there is flickering when you switch between a normal folder icon and a previews folder icon, in particular if you expand the information panel. Can you try to fix that?
I guess you mean the transition animation between the two preview (icon and preview).
The animation is good eye-candy when switching between two very different previews, from a file preview to a folder preview for instance.
And I would argue that this is valuable when switching between folder preview and folder icon, because it informs the user, the preview has been updated.