Not necessarily related to follows but an interesting metric that is unique to nostr would be something like count of different kind events within a month.

For example:

If you only publish Kind 1

You account will show Engagement 1

But if you engage in nests, streams, highlighter, etc…

Your account will show Engagement 7.

Now make this cool and subtitle the number with a fun temperature gauge or something and you have your self something unique to nostr. nostr:note1qkakcjnct6j67chyg596ked4n4nutyp9e6k35s6ly3w3ssc4wuxq2harxs