The topic list is structured as a table, so I think it would be impossible to do this in CSS. You’d need to write a plugin that hijacks the topic-list template and the topic-list-item method to create <div>s instead. No small task.
EDIT: Hang on, you can’t display: inline-block a <tr> can you? that might work.
Yes it does work. Styling each card would be a bottomless pit of CSS despair, but I believe it can be done. Combine with the Topic List Previews plugin and you’d get an excerpt on each card.
Actually it might be due to it using the Mobile view. And prior to today, Mobile view templates couldn’t be overridden. So now that they can be, he might already be working on that.