The actualy JAR won't contain the JFunction class.

At the moment this class is gone missing. It's neither on RC3 nor will it be included in the publishLocal jar.
But it will be generated. it just looks like the publish task won't add src_managed classes?

Edit:

OsgiKeys.exportPackage := Seq(s"scala.compat.java8.*;version=${version.value}", s"scala.runtime.java8.*;version=${version.value}"),

needs to be set, however it should probably include a switch for < 2.12