When subscribing to a normal text-only rss feed (not a podcast), it usually does not have an icon. I think adding full UI+database for setting custom icons is a bit too much (especially since text-only feeds are not officially supported anyway). Maybe it would be nice to add some generative art as thumbnails when the feed does not have an image.
Something similar to the default GitHub profile pictures that are randomly generated patterns. Alternatively, something like this: https://generative-placeholders.glitch.me/
What do you think?