This is great! I bet authors will love them. I've got in the habit of making fic banners for longer fics at AO3 because they're better for promoting at Tumblr (visuals always do better) and you can add them to Pinterest etc. I make fic 'covers' for my original works at Wordpress for the same reason, eye catching and promotional material :) So I think it's great that you're doing this for yourself and for other people, and I hope it helps people find the podfic they're looking for, and helps promote the works further :