If you're only going to take one person's usage then, yeah, I guess it's pretty narrow. How about another example for from the same person. As a video editor I'm constantly having to find "hip/trendy/cool" music for video edits. These clients typically like music that I do not normally listen to, but I know it's something they would like when I hear it. I'll let it live in My Shazams until one day I need to find something. I've impressed more than one client with the ability to pull out a "fresh" song for them. Clients appreciate that sort of thing.
How about it? We've just added video editor looking for cool music to DJ. We could add tens such cases more, but all those combined are still narrow demographics.
Also, diabetes narrow? 30 million have it in the US, I'd say those are way more than DJs that need to recognize tunes, and have much more motive to use an app that helps them keep track of something that can have huge impact on their health...
So a pretty narrow demographic for the feature though...