Angelo,
Thank you for the response! I've started using the "Featured Images in RSS & Mailchimp Email" plugin, but it applies only to the main WordPress feed; it does not alter the podcast feed generated by PowerPress.
I'd like for my podcast feed to offer the featured image and the album artwork separately; I don't want to offer unique album artwork on a per-episode basis. Providing the featured image in the RSS feed would allow RSS aggregators, RSS-to-mail campaigns in MailChimp, and other services to have a featured image to work with, instead of using my album artwork for each post.
The way the "Featured Images in RSS & Mailchimp Email" plugin does this is by prepending an <img> tag with the featured image to the post's body in the RSS feed. Maybe something similar could be an option in PowerPress?
That said, I could see using the featured image as album artwork would be useful, even if not in my exact scenario; that option would also be a welcome addition, as you suggested.
-Ken