So as a team that builds and deploys 100% Clojure, what is the impetus for us to move from JDK 1.8 to 1.9 or even 1.10? Are there any performance boosts in later JDKs? What about pitfalls?
We’re currently moving from Clojure 1.8 to 1.9.
I would say no. Wait for Java 11, which will be the next long term release.
The only good reason to move to Java 9 now would be if you want to bundle a smaller JVM with your app.
On the Clojure front, some tooling was having issues with Java 9, I think most are resolved now with their latest version, that does mean you might need to upgrade them.
P.S.: Java 10 is already released by the way.
To add some more information, Java 9 stops getting public updates in March 2018 which is now. Unless there is a pressing reason to use Java 9, like @didibus said, wait for Java 11.