You can change the album art with Chapter Art defined in the podcast feed.
That way the audio track would remain “whole” and the xml feed would do the work of changing album covers.
I do not know the frequency of changes (see the chapter length) you can make, or if there are any limits to the numbers of chapters per podcast.
Assuming a high enough frequency is permissible, you might get your shot at “video” again.
Check out the ATP.fm podcast - they occasionally use chapter art.
Also, checkout Forecast by Overcast which can help you set chapter art.
Good luck with your venture!!