I wonder whether we could drop support for Java 5 runtime with the following benefits:

• Simplify test/build setup: With the advent of Java 9 we're now testing on 5 different JDK versions.
• Allow dynamic attachment of JaCoCo agent
• Simplify runtime data access
• allow coverage on bootstrap classes
• support re-transformation (no schema changes any more)

The last three become possible by adding companion classes to the bootstrap classpath with new method java.lang.instrument.Instrumentation.appendToBootstrapClassLoaderSearch().