> Now GraalVM provides a polyglot runtime for JavaScript and Ruby, but my understanding is it'll be commercial-only once it's released. So in a way, Oracle is preparing a Java exit strategy themselves :)

Your understanding is wrong.

GraalVM comes in two editions: Community Edition (CE) and Enterprise Edition (EE) (https://www.graalvm.org/downloads/).

Community Edition is open-source (https://github.com/oracle/graal) and has a relatively permissive license (GPL v2 + Classpath exception, all source files have the Classpath exception). The Classpath exception was added recently and will make a world of a difference.

Enterprise Edition provides additional optimizations and commercial support. Nevertheless, CE will take you a long way. Twitter says they have achieved a 12% speedup in the real world by running their Scala services with CE's Graal JIT.

All language implementations have been open-sourced by now (except for some EE optimizations). Most of them (including Graal.js and TruffleRuby) are licensed under Universal Permissive License or Eclipse Public License.

My favorite use of GraalVM is creating native executables with Substrate VM. Works great and brings startup time of my Java/Kotlin command-line applications down to 1 ms.