I've had preliminary discussions with some Groovy core developers and they are receptive to having JSR 354 support as a "Groovy Module" and possibly, once JSR 354 is final (or shipped with Java 9?) even a core module. A reasonable name for such a module would be groovy-money, it would seem.
It seems like a natural place for the Groovy support code to end up.
What do others think?