JavaPoly uses Doppio. As a result, you can run both Rhino and Nashorn in JavaPoly too!
Awesome, and can we run Doppio in Rhino run in Doppio then? Recursive Atwood's law!
Haha, I've actually tried to do this. The only missing link, I believe, is to add a Nashorn/Rhino backend to BrowserFS (Doppio's file system library) so that Doppio can access the filesystem that Rhino is running in to load the JDK.
If that sounds like fun, I take pull requests [0]. :)
(I'm the primary author of Doppio.)