As this is default behavior, I’ve made this default behavior in this plugin as well.
I’ve added this as a setting. It’s off by default.
I’ve added a setting so you can change the topic excerpt character length. Keep in mind that there is a maximum height of topic list items of 100px and that, regardless of excerpt length, the space afforded for the excerpt will be determined by the space left over after the combined height of the topic list elements in the main topic list item column are subtracted from 100. For example, if you have the category badge move setting enabled, then the category badge will appear in the main topic list item column, reducing the space available for the excerpt. We could also allow the maximum height of the topic list items to be a setting, however that is a slightly different issue.
I’ve added the ‘fallback’ part of this. You can now set a default thumbnail on a site-wide or per-category basis.
Finally, it seems as though the core functionality is solid enough for this to move to v0.2. This doesn’t mean that there won’t be issues in the future, but, as you can see from this update, further developments are relatively contained (i.e. they don’t require significant refactoring).