Thanks! Also, since I've published this progress update, more work has been completed on the Floor Browser's design. Now it's mostly complete, as you can see in the development image below.
Yes, they will be changed to show a preview image of that custom floor. Although if the background image for that floor entry was unable to be loaded for some reason in the browser, it will show a placeholder thumbnail instead as a backup. As for what the preview backgrounds will look like, here's a look at one of them.