As a reader, I’ve grown quite fond of the subscribe features, both for authors and series. It’s made my day multiple times to get an email notifying me that a story I was especially anticipating just got posted.
As an author, I think it could be interesting and motivating to know how many people, if any, have subscribed - knowing that x number of people will get a notification about the story immediately. And, it also might encourage readers to use the feature more if they know the author will see it.
I’m not suggesting in any way that subscribes should be used as any kind of overall metric for stories, and certainly shouldn’t be public. But as an author, I’d find it at least exciting to know, and might even provide some useful feedback.