I thought "I want one of those" so set about adding new code to the Today template to generate a "Daily feed" just as I do with "On this day" - hence breaking things by uploading a wrong version.
A cron job runs at 5 minutes past midnight every day to silently load the Today page thus triggering the code to build the RSS feeds and saves the files to the root of the site.
I think I'm there but want to check if it works correctly before linking to it - I think I'll update the /Subscribe page with both these above feeds (not that I anticipate anyone subscribing, it's really just a vanity project) once I'm happy that everything works as it should.
get_the_content_feed('rss2')to format it correctly for the feed rather than just
get_the_content()- all good now.