If it’s really what is described (an app that other apps can use to classify content without querying a server), seems like a good thing to me. There is a clear need for people to be able to filter spam and things they don’t want to see. Imagine a Lemmy app where you can set it to not show you US politics related posts, where it will work regardless of whether specific keywords are in the title. Couldn’t that kind of thing contribute to a more decentralized web?