Hopefully, OpenJDK would be less fractured than Linux. One thing to note, though, is that you can only call your JDK "OpenJDK" if it's a build of the OpenJDK project, with no substantial additions or removal of code[1]. Most free JDKs are, indeed, OpenJDK, with the exception of the JDK based on IBM's OpenJ9 JVM, even though it uses parts of the OpenJDK codebase.

[1]: http://openjdk.java.net/legal/openjdk-trademark-notice.html

AdoptOpenJDK will be working with Amazon and the other providers to make sure there's some consistency between the binaries, no point in fragmenting all over the place, consumers expect to be able to drop in replacements.

Unsafe is still accessible even in JDK 11. May require some command-line flags, though.