> you MUST learn Clojure (which can be hard to get a whole team to agree to)

For any sufficiently advanced monitoring system, you're going to have to learn some form of DSL/language to take advantage of it.

I wouldn't consider this to be a major issue, more part of the irreducible complexity of the problem. The Riemann examples I've seen all seemed pretty readable, and routing alerts is not world away from what you'd be doing in say a Prometheus Alertmanager config; just with S-Expressions against YAML.