One thing I've noticed with podcasts, is that my reader will download the full RSS every day, listing hundreds of episodes, just to see if there's a new one.

I get why they do this as a new listener will want to start off with a full list of episodes and may want to pick up a show from the start.

It would be useful if an RSS could specify a separate URL to query that will only list new episodes, returning an empty RSS (or a standardized HTTP status code) until the new episode is available.

The original RSS with the full list would still be the primary URL for the podcast, the one I get when I right-click and select "Copy RSS URL".