To my mind the predominant value of PKI RSS encryption would be for authentication rather than confidentiality.
But what if I wanted to build a set of RSS feeds that matches my stock portfolio - I need authentication so that I get my portfolio and not somebody elses, and I need confidentiality because there is value in the selection of stocks that form my portfolio. Particularly if we're talking about a research portfolio, then the selection of stocks may be valuable and confidential. (in fact in some circumstances, I may be required to keep them confidential to avoid accusations of insider trading).
There may also be use cases in the field of medicine. I may not wish to publicly advertise the set of diseases/drugs/treatments that I'm tracking and researching.