Duplicate articles are more related to https://bazqux.uservoice.com/forums/190752-general/suggestions/4169270-add-a-way-to-identify-duplicate-articles-i-e-sam
Although it's about articles in different feeds.

You could mail me these feeds so I could take a look. In general BazQux is trying to ignore duplicated articles.

This would be very useful to me. I have some, shall we say, "less-than-intelligent" feeds that have an annoying habit of coughing up the same entry multiple times, and at least one that will rehash 10-20 old items whenever a new one comes in... The latter would benefit by filtering out pubdates over a certain time period old, while both could be solved by duplicate link, title, content, or pubdate fields.

Unfortunately, I can't yet say when I get to it. But I defeinitely plan to add subscriptions management

Any update on this?

Or maybe a warning sign beside the name of the feed when updating is failing.

I'm planning to make some kind of subscription management. It mostly for removing old feeds that aren't updated. But I can include an option to find duplicates too.

The feeds probably had slight differences in the url like http vs. https and/or different query on the end of the url.

Baz sees them as different URLs even though they are the same feed.

Would it be possible for the service to detect different URLs that are providing the same exact feeds and do some kind of duplication detection?

Example:
http://feeds.feedburner.com/CitizenRadio
http://feeds.feedburner.com/CitizenRadio?format=xml

That's strange. Feeds with the same URL should not be duplicated. Are duplicated feeds have the same URL (right click on the feed and then "Feed address") ?

Or maybe feeds are in different folders?

BTW: you can subscribe to your YouTube subscriptions using http://gdata.youtube.com/feeds/api/users/USERNAME/newsubscriptionvideos
(more about it here http://blog.bazqux.com/2015/06/subscribing-to-youtube-feeds.html )