What poweruser tools are you missing in newsboat?
I've started working on my own "power user" RSS reader that lets you weight the keywords you're interested in (so an article that hits important keywords but is older could be displayed above an article that's newer) but it's still closer to a proof-of-concept than a complete app.
Originally that would have been mutt, later my own client, and later still I switched to gsuite.
I did add support for excluding entries/posts based on title, body, regular expression, and similar, but at the end of the day I just fetch all feed entries and save them as emails. The later processing can be done by any client and that's pretty flexible. There's very little custom processing required in the RSS-processing itself.