cl-uglify-js is not changed for quite some time, while uglify-js is being actively developed. Do you have any plan to sync them to a latest version? That will keep cl-uglify-js active and add many new improvements into it.
Well, many of the new features in the JS version were driven by contributors—when a bug was found, it was reported; sometimes even fixed and I just merged the patch. Sadly this doesn't happen with the CL version :-( but it still works well enough for me (I'm using it in production systems).
If you need a certain feature, or find a bug, please file a ticket on it and I'll do if/when I can.