Have one project still using JDK8 which will migrate in January (just one library that needs a version upped), everything else is already JDK11 and working without issues.
Using Kotlin, so the Java version doesn't really bring much to the table other than security and performance. I believe Kotlin compiles to JDK8 compatible binaries anyways for the moment, but will be making the jump to 11 soon.
JDK 9 and 10 seems to be a lost generation, nobody's using them :-D