This is turning out to be a bit more involved. Mostly because I have no experience in generating rss...
Newsboat filters operate on the whole feed. So the script needs to read the input rss (cf feedparse) then retrieve the HTML (cf rdrview) and then generate rss errrr.... Feedparse doesn't do that last bit.
And then add a layer of on disk caching because otherwise it would keep re-downloading all entries over and over again.
I'll get back to that tomorrow I guess. Now for shut-eye