The jerboa app does this, and it helps when searching for a community to see how many people use it, especially when there are multiple across different instances.
That said, I don’t really know how accurate their number is so maybe it’s not super viable
It’s a reasonable feature request and with this discussion thread some of the invisible complexity is exposed a bit for consideration. I think it’s sensible to leave the post up, and the dev(s) can decide what to prioritize and how they want to design something like this if they choose to work on it.