Nevertheless we are blocked by some issues in Rhino that don’t get fixed – or not quickly enough – even when we propose patches (for instance bug 412928). As discussed in Rhino mailing list  this seems to come from a lack of resources on Rhino’s side as well as from a slightly different focus: for us the most important is to simulate browser’s behaviour whereas speed and respect of ECMA standard are very important for Rhino.
Releases of htmlunit-core-js will be made available at the same time than future HtmlUnit releases.
My biggest hope for this project is… to be able to declare it dead and useless as soon as possible, once Rhino fills all our need. For this purpose, we will continue to open issues and provide patches to the Rhino project to help improving it.
 Rhino mailing list thread “Rhino project (half) asleep?“