It's used everywhere. Just because Google killed their RSS reader at a time - it didn't die. I use it for pretty much all my news, updates from sites. If a site doesn't provide feed, I won't bother visiting it and checking for updates. And I host it myself with miniflux + postgresql.
Sure, lots and lots of them!!
hnrss.org
I mean sure there are official ones.
https://news.ycombinator.com/rss
However HNRSS is the best way to do HN feeds.