Hey! Great extension, thanks for picking it up. It really adds nice look and feel to Flarum's main page. I tried it on my test installation and here's a couple of suggestions if I may.
First one, it's not always a great idea to make unread topic the only one with color image. A whole page full of b/w images could look not so nice. But it's still very important to see what topic has some unread posts. So it would be nice to add just a bit of default Flarum behavior here:
I.e. make read topics with a thinner title and add number of answers at a more familiar place. Also it's very useful to see who and when answered in the topic. So it would be great to return the string "username replied X time ago" to the cards.
If these are implemented I would be happy to use the extension on production site!