sounds like this is limited by redis. For many organizations, this is fine. At my last gig, we used redis for deduplication and it required over 150 redis nodes with deterministic routing and consensus. Redis reportedly could support 200k rps per node, but in our case, we wouldn't see it get passed around 50k rps no matter how we tuned it.
An interesting addition to this library would be to use an interface and allow your backing datastore of choice allowing teams to use redis, zookeeper, an in-mem Go instance of the same library, sql, etc.
A fun exercise would be to figure out how to make the rate limiting itself distributed so you don't need a single store keeping everything in sync. Maybe a combo of deterministic request routing in a ring topology