Scala BitSet implemented with Java BitSet, for use in Scala Enumerations to replace ValueSet
After studying your code for a good long while, I realized that the reason you haven't gotten an answer is that there isn't really much to say about your code. Well done!

I would recommend adding some thorough ScalaDoc though. It has been my experience that Scala library developers have far too much faith in the ability of library users to magically understand what they really meant. Examples are wonderful things.