Google has historically provided an unofficial endpoint to access an RSS feed of videos for a given YouTube channel, at "https://www.youtube.com/feeds/videos.xml?channel_id=your_id_here". As of today it seems to be 404. Is this intentional and permanent? If so, it's a loss for the open web, and it seems like a lot of feed readers, website widgets and other tools depending on this endpoint will be unhappy very soon.
Edited to add: looks like this feature is back online now, 21:05 UTC Monday. Glad it was temporary!