> Even for sites that don't offer granular feeds, every major feed reader offers filtering options, a lot of them offer fairly complex regex filtering.

This is true to some degree, but regex filtering or really any strictly logical filtering is often too coarse or too fragile to work well in practice for all but the most dedicated RSS gardeners.

What I’d really like to see is some sort of fuzzier logic that gives the user a more semantic interface to filtering and/or ranking feed items.

Take, for example, the feed for a medium-sized newspaper where you want to filter for/prioritize articles about your local area and particular topics of interest. Those news feeds are often very high volume and don’t make good use of tags or other metadata that can be consumed by strictly logical filtering systems. So a fragile, badly-behaving filtered list is what you’re likely to get. Whereas a fuzzier, more semantic interface (local LLMs?) would be far more reliable and easier to use.