RSS can become very messy super quickly, and I think we need clients that don't look like the ones we know from 15 years ago, but ones that help users to keep their subscriptions neat and clean.
This is quite what RSS needs: Killer usecases for the Z generation. And podcasts are only halfway fashionable. Instagram, OnlyFans… it seems RSS needs a payment model to be fashionable ;)
Entirely replaced by link-voting sites now, like HN.
They had some other RSS feeds than for channels and playlists?
There's a Reeder 5 and the two improvements (for me) that it has over 3 is that Twitter probably won't say "outdated browser" and refuse to show tweets and support for adding newsfeeds directly. I think MacOS added support for this after Reeder 3 was released.
Mixing the two readers is fine because Feedly is keeping track for them. If Feedly were to start charging, I'd probably start using NNW exclusively since they provide the option of using iCloud to sync.
To me RSS and the reader are and should be separate.
RSS is the protocol to query and retrieve updated articles. The reader can be anything you like.
Personally I use rss2email for retrieval and my UI is my email app.