I'd really like that feature.
since the introduction of custom post types and custom taxonomies I have added some to my blog.
I have also edited my functions.php to show posts from different categories,pages and recipes (my custom post type) on the front page and in my feed.
now I'd love to add a custom image/icon that will help visitors visually distinguish between posts from the tech category and a recipe and your plugin sounds great.
Of course this can be done by editing my theme template files and some custom css too...