Please make all def underlying public in jcl.*, so it could be possible to write something like:

===
import scala.collection.jcl

// some external java library method that accepts j.u.Collection
def someJavaLibraryMethod(c: java.util.Collection) = ()

// my function that returns collection. I do not want to specify what concrete collection I return
def someMyFunction: jcl.CollectionWrapper[Int] = new jcl.ArrayList[Int]

val l = someMyFunction

someJavaLibraryMethod(l.underlying)
===

error: method underlying cannot be accessed in scala.collection.jcl.CollectionWrapper[Int]

This change will also make easier to write implicit converters from jcl collections to java.util collections.