I know of the ‘Playback history’ in Settings/Sliding menu"… but that only shows playback history of podcasts you have listened to, that are currently downloaded … a "Subscription History" would be great. I've had SO many audiobooks downloaded, & then deleted because keeping them once listened to, takes up way too much space in phone… but when I'm searching for new podcasts/audiobooks, there's no way to tell if I've downloaded it previously. If there was something like a little icon in the thumbnail corner (like the green tick), that appears on any podcast you've ever listened to, it'd save precious data from being wasted by downloading podcasts that you've forgotten you'd already downloaded once before & deleted…. & would help for finding them if you want to re-download for another listen!
Thanks for taking the time to read my suggestion!

(Edit: for manners)