"List view" and "Mosaic view" should also display "mark as unread" button.
I use "Mark read on scroll", but some itens I restore as unread when I think it's something like "read it later, but not late enough to deserve a star". Like "read it later, but today".
I use "List view" for some feeds/folders and "Mosaic view" for others, and these two view modes are the only ones without a visible button to mark as unread (without the need to expand the item).
I think the circle button to mark as unread should be visible for these two view modes too. This small change would help a lot without disturbing anything.
Note: I think it would be better if this button were positioned on the left side, near the star. But this is a minor detail.
I've added marking read/unread with Shift+Click on the post image in mosaic/magazine view.
It's possible to toggle read state using Shift+Click in list view. But not yet in mosaic. I will add it too